# bash

## NAME



           bash - GNU Bourne-Again SHell
    


## SYNOPSIS



           **bash**[options] [command_string | file]
    


## DESCRIPTION



           **Bash** is a command language interpreter that executes commands read
           from the standard input, from a string, or from a file.  It is a
           reimplementation and extension of the Bourne shell, the historical
           Unix command language interpreter.  **Bash** also incorporates useful
           features from the _Korn_ and _C_ shells (**ksh** and **csh**).
    
           POSIX is the name for a family of computing standards based on
           Unix.  **Bash** is intended to be a conformant implementation of the
           Shell and Utilities portion of the IEEE POSIX specification (IEEE
           Standard 1003.1).  **Bash** POSIX mode (hereafter referred to as _posix_
           _mode_) changes the shell's behavior where its default operation
           differs from the standard to strictly conform to the standard.
           See **SEE ALSO** below for a reference to a document that details how
           posix mode affects **bash** 's behavior.  **Bash** can be configured to be
           POSIX-conformant by default.
    


## OPTIONS



           All of the single-character shell options documented in the
           description of the **set** builtin command, including **-o** , can be used
           as options when the shell is invoked.  In addition, **bash**
           interprets the following options when it is invoked:
    
           **-c** If the **-c** option is present, then commands are read from
                  the first non-option argument _command_string_.  If there are
                  arguments after the _command_string_ , the first argument is
                  assigned to **$0** and any remaining arguments are assigned to
                  the positional parameters.  The assignment to **$0** sets the
                  name of the shell, which is used in warning and error
                  messages.
    
           **-i** If the **-i** option is present, the shell is _interactive_.
    
           **-l** Make **bash** act as if it had been invoked as a login shell
                  (see **INVOCATION** below).
    
           **-r** If the **-r** option is present, the shell becomes _restricted_
                  (see **RESTRICTED SHELL** below).
    
           **-s** If the **-s** option is present, or if no arguments remain
                  after option processing, the shell reads commands from the
                  standard input.  This option allows the positional
                  parameters to be set when invoking an interactive shell or
                  when reading input through a pipe.
    
           **-D** Print a list of all double-quoted strings preceded by **$** on
                  the standard output.  These are the strings that are
                  subject to language translation when the current locale is
                  not **C** or **POSIX**.  This implies the **-n** option; no commands
                  will be executed.
    
           **[-+]O [**_shopt_option_**]**
                  _shopt_option_ is one of the shell options accepted by the
                  **shopt** builtin (see **SHELL BUILTIN COMMANDS** below).  If
                  _shopt_option_ is present, **-O** sets the value of that option;
                  **+O** unsets it.  If _shopt_option_ is not supplied, **bash** prints
                  the names and values of the shell options accepted by **shopt**
                  on the standard output.  If the invocation option is **+O** ,
                  the output is displayed in a format that may be reused as
                  input.
    
           **--** A **--** signals the end of options and disables further option
                  processing.  Any arguments after the **--** are treated as a
                  shell script filename (see below) and arguments passed to
                  that script.  An argument of **-** is equivalent to **--**.
    
           **Bash** also interprets a number of multi-character options.  These
           options must appear on the command line before the single-
           character options to be recognized.
    
           **--debugger**
                  Arrange for the debugger profile to be executed before the
                  shell starts.  Turns on extended debugging mode (see the
                  description of the **extdebug** option to the **shopt** builtin
                  below).
    
           **--dump-po-strings**
                  Equivalent to **-D** , but the output is in the GNU _gettext_ “po”
                  (portable object) file format.
    
           **--dump-strings**
                  Equivalent to **-D**.
    
           **--help** Display a usage message on standard output and exit
                  successfully.
    
           **--init-file** _file_
           **--rcfile** _file_
                  Execute commands from _file_ instead of the standard personal
                  initialization file _~/.bashrc_ if the shell is interactive
                  (see **INVOCATION** below).
    
           **--login**
                  Equivalent to **-l**.
    
           **--noediting**
                  Do not use the GNU **readline** library to read command lines
                  when the shell is interactive.
    
           **--noprofile**
                  Do not read either the system-wide startup file
                  _/etc/profile_ or any of the personal initialization files
                  _~/.bash_profile_ , _~/.bash_login_ , or _~/.profile_.  By default,
                  **bash** reads these files when it is invoked as a login shell
                  (see **INVOCATION** below).
    
           **--norc** Do not read and execute the personal initialization file
                  _~/.bashrc_ if the shell is interactive.  This option is on
                  by default if the shell is invoked as **sh**.
    
           **--posix**
                  Enable posix mode; change the behavior of **bash** where the
                  default operation differs from the POSIX standard to match
                  the standard.
    
           **--restricted**
                  The shell becomes restricted (see **RESTRICTED SHELL** below).
    
           **--verbose**
                  Equivalent to **-v**.
    
           **--version**
                  Show version information for this instance of **bash** on the
                  standard output and exit successfully.
    


## ARGUMENTS



           If arguments remain after option processing, and neither the **-c**
           nor the **-s** option has been supplied, the first argument is treated
           as the name of a file containing shell commands (a _shell script_).
           When **bash** is invoked in this fashion, **$0** is set to the name of the
           file, and the positional parameters are set to the remaining
           arguments.  **Bash** reads and executes commands from this file, then
           exits.  **Bash** 's exit status is the exit status of the last command
           executed in the script.  If no commands are executed, the exit
           status is 0.  **Bash** first attempts to open the file in the current
           directory, and, if no file is found, searches the directories in
           **PATH** for the script.
    


## INVOCATION



           A _login shell_ is one whose first character of argument zero is a
           **-** , or one started with the **--login** option.
    
           An _interactive shell_ is one started without non-option arguments
           (unless **-s** is specified) and without the **-c** option, and whose
           standard input and standard error are both connected to terminals
           (as determined by isatty(3)), or one started with the **-i** option.
           **Bash** sets **PS1** and **$-** includes **i** if the shell is interactive, so a
           shell script or a startup file can test this state.
    
           The following paragraphs describe how **bash** executes its startup
           files.  If any of the files exist but cannot be read, **bash** reports
           an error.  Tildes are expanded in filenames as described below
           under **Tilde Expansion** in the **EXPANSION** section.
    
           When **bash** is invoked as an interactive login shell, or as a non-
           interactive shell with the **--login** option, it first reads and
           executes commands from the file _/etc/profile_ , if that file exists.
           After reading that file, it looks for _~/.bash_profile_ ,
           _~/.bash_login_ , and _~/.profile_ , in that order, and reads and
           executes commands from the first one that exists and is readable.
           The **--noprofile** option may be used when the shell is started to
           inhibit this behavior.
    
           When an interactive login shell exits, or a non-interactive login
           shell executes the **exit** builtin command, **bash** reads and executes
           commands from the file _~/.bash_logout_ , if it exists.
    
           When an interactive shell that is not a login shell is started,
           **bash** reads and executes commands from _~/.bashrc_ , if that file
           exists.  The **--norc** option inhibits this behavior.  The **--rcfile**
           _file_ option causes **bash** to use _file_ instead of _~/.bashrc_.
    
           When **bash** is started non-interactively, to run a shell script, for
           example, it looks for the variable **BASH_ENV** in the environment,
           expands its value if it appears there, and uses the expanded value
           as the name of a file to read and execute.  **Bash** behaves as if the
           following command were executed:
    
                  if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
    
           but does not use the value of the **PATH** variable to search for the
           filename.
    
           If **bash** is invoked with the name **sh** , it tries to mimic the startup
           behavior of historical versions of **sh** as closely as possible,
           while conforming to the POSIX standard as well.  When invoked as
           an interactive login shell, or a non-interactive shell with the
           **--login** option, it first attempts to read and execute commands
           from _/etc/profile_ and _~/.profile_ , in that order.  The **--noprofile**
           option inhibits this behavior.  When invoked as an interactive
           shell with the name **sh** , **bash** looks for the variable **ENV** , expands
           its value if it is defined, and uses the expanded value as the
           name of a file to read and execute.  Since a shell invoked as **sh**
           does not attempt to read and execute commands from any other
           startup files, the **--rcfile** option has no effect.  A non-
           interactive shell invoked with the name **sh** does not attempt to
           read any other startup files.
    
           When invoked as **sh** , **bash** enters posix mode after reading the
           startup files.
    
           When **bash** is started in posix mode, as with the **--posix** command
           line option, it follows the POSIX standard for startup files.  In
           this mode, interactive shells expand the **ENV** variable and read and
           execute commands from the file whose name is the expanded value.
           No other startup files are read.
    
           **Bash** attempts to determine when it is being run with its standard
           input connected to a network connection, as when executed by the
           historical and rarely-seen remote shell daemon, usually _rshd_ , or
           the secure shell daemon _sshd_.  If **bash** determines it is being run
           non-interactively in this fashion, it reads and executes commands
           from _~/.bashrc_ , if that file exists and is readable.  **Bash** does
           not read this file if invoked as **sh**.  The **--norc** option inhibits
           this behavior, and the **--rcfile** option makes **bash** use a different
           file instead of _~/.bashrc_ , but neither _rshd_ nor _sshd_ generally
           invoke the shell with those options or allow them to be specified.
    
           If the shell is started with the effective user (group) id not
           equal to the real user (group) id, and the **-p** option is not
           supplied, no startup files are read, shell functions are not
           inherited from the environment, the **SHELLOPTS** , **BASHOPTS** , **CDPATH** ,
           and **GLOBIGNORE** variables, if they appear in the environment, are
           ignored, and the effective user id is set to the real user id.  If
           the **-p** option is supplied at invocation, the startup behavior is
           the same, but the effective user id is not reset.
    


## DEFINITIONS



           The following definitions are used throughout the rest of this
           document.
           **blank** A space or tab.
           **whitespace**
                  A character belonging to the **space** character class in the
                  current locale, or for which isspace(3) returns true.
           **word** A sequence of characters considered as a single unit by the
                  shell.  Also known as a **token**.
           **name** A _word_ consisting only of alphanumeric characters and
                  underscores, and beginning with an alphabetic character or
                  an underscore.  Also referred to as an **identifier**.
           **metacharacter**
                  A character that, when unquoted, separates words.  One of
                  the following:
                  **| & ; ( ) < > space tab newline**
           **control operator**
                  A _token_ that performs a control function.  It is one of the
                  following symbols:
                  **|| & && ; ;; ;& ;;& ( ) | |& <newline>**
    


## RESERVED WORDS



           _Reserved words_ are words that have a special meaning to the shell.
           The following words are recognized as reserved when unquoted and
           either the first word of a command (see **SHELL GRAMMAR** below), the
           third word of a **case** or **select** command (only **in** is valid), or the
           third word of a **for** command (only **in** and **do** are valid):
    
           **! case  coproc  do done elif else esac fi for function if in**
           **select then until while { } time [[ ]]**
    


## SHELL GRAMMAR



           This section describes the syntax of the various forms of shell
           commands.
    
       **Simple Commands**
           A _simple command_ is a sequence of optional variable assignments
           followed by **blank** -separated words and redirections, and terminated
           by a _control operator_.  The first word specifies the command to be
           executed, and is passed as argument zero.  The remaining words are
           passed as arguments to the invoked command.
    
           The return value of a _simple command_ is its exit status, or 128+_n_
           if the command is terminated by signal _n_.
    
       **Pipelines**
           A _pipeline_ is a sequence of one or more commands separated by one
           of the control operators **|** or **| &**.  The format for a pipeline is:
    
                  [**time**[**-p**]] [ ! ] _command1_ [ [**|** ⎪**| &**] _command2_ ... ]
    
           The standard output of _command1_ is connected via a pipe to the
           standard input of _command2_.  This connection is performed before
           any redirections specified by the _command1_(see **REDIRECTION** below).
           If **| & **is the pipeline operator, _command1_ 's standard error, in
           addition to its standard output, is connected to _command2_ 's
           standard input through the pipe; it is shorthand for **2 >&1 |**.  This
           implicit redirection of the standard error to the standard output
           is performed after any redirections specified by _command1_.
    
           The return status of a pipeline is the exit status of the last
           command, unless the **pipefail** option is enabled.  If **pipefail** is
           enabled, the pipeline's return status is the value of the last
           (rightmost) command to exit with a non-zero status, or zero if all
           commands exit successfully.  If the reserved word **!** precedes a
           pipeline, the exit status of that pipeline is the logical negation
           of the exit status as described above.  If a pipeline is executed
           synchronously, the shell waits for all commands in the pipeline to
           terminate before returning a value.
    
           If the **time** reserved word precedes a pipeline, the shell reports
           the elapsed as well as user and system time consumed by its
           execution when the pipeline terminates.  The **-p** option changes the
           output format to that specified by POSIX.  When the shell is in
           posix mode, it does not recognize **time** as a reserved word if the
           next token begins with a “-”.  The value of the **TIMEFORMAT**
           variable is a format string that specifies how the timing
           information should be displayed; see the description of **TIMEFORMAT**
           below under **Shell Variables**.
    
           When the shell is in posix mode, **time** may appear by itself as the
           only word in a simple command.  In this case, the shell displays
           the total user and system time consumed by the shell and its
           children.  The **TIMEFORMAT** variable specifies the format of the
           time information.
    
           Each command in a multi-command pipeline, where pipes are created,
           is executed in a _subshell_ , which is a separate process.  See
           **COMMAND EXECUTION ENVIRONMENT** for a description of subshells and a
           subshell environment.  If the **lastpipe** option is enabled using the
           **shopt** builtin (see the description of **shopt** below), and job
           control is not active, the last element of a pipeline may be run
           by the shell process.
    
       **Lists**
           A _list_ is a sequence of one or more pipelines separated by one of
           the operators **;** , **&** , **& &**, or **||** , and optionally terminated by one of
           **;** , **&** , or **< newline>**.
    
           Of these list operators, **& & **and **||** have equal precedence, followed
           by **;** and **&** , which have equal precedence.
    
           A sequence of one or more newlines may appear in a _list_ instead of
           a semicolon to delimit commands.
    
           If a command is terminated by the control operator **&** , the shell
           executes the command in the _background_ in a subshell.  The shell
           does not wait for the command to finish, and the return status is
           0.  These are referred to as _asynchronous_ commands.  Commands
           separated by a **;** are executed sequentially; the shell waits for
           each command to terminate in turn.  The return status is the exit
           status of the last command executed.
    
           AND and OR lists are sequences of one or more pipelines separated
           by the **& & **and **||** control operators, respectively.  AND and OR
           lists are executed with left associativity.  An AND list has the
           form
    
                  _command1_ **& & **_command2_
    
           _command2_ is executed if, and only if, _command1_ returns an exit
           status of zero (success).
    
           An OR list has the form
    
                  _command1_ **||**_command2_
    
           _command2_ is executed if, and only if, _command1_ returns a non-zero
           exit status.  The return status of AND and OR lists is the exit
           status of the last command executed in the list.
    
       **Compound Commands**
           A _compound command_ is one of the following.  In most cases a _list_
           in a command's description may be separated from the rest of the
           command by one or more newlines, and may be followed by a newline
           in place of a semicolon.
    
           (_list_) _list_ is executed in a subshell (see **COMMAND EXECUTION**
                  **ENVIRONMENT** below for a description of a subshell
                  environment).  Variable assignments and builtin commands
                  that affect the shell's environment do not remain in effect
                  after the command completes.  The return status is the exit
                  status of _list_.
    
           { _list_ ; }
                  _list_ is executed in the current shell environment.  _list_
                  must be terminated with a newline or semicolon.  This is
                  known as a _group command_.  The return status is the exit
                  status of _list_.
    
                  Note that unlike the metacharacters **(** and **)** , **{** and **}** are
                  _reserved words_ and must occur where a reserved word is
                  permitted to be recognized.  Since they do not cause a word
                  break, they must be separated from _list_ by whitespace or
                  another shell metacharacter.
    
           ((_expression_))
                  The arithmetic _expression_ is evaluated according to the
                  rules described below under **ARITHMETIC EVALUATION**.  If the
                  value of the expression is non-zero, the return status is
                  0; otherwise the return status is 1.  The _expression_
                  undergoes the same expansions as if it were within double
                  quotes, but unescaped double quote characters in _expression_
                  are not treated specially and are removed.  Since this can
                  potentially result in empty strings, this command treats
                  those as expressions that evaluate to 0.
    
           **[[**_expression_ **]]**
                  Evaluate the conditional expression _expression_ and return a
                  status of zero (true) or non-zero (false).  Expressions are
                  composed of the primaries described below under **CONDITIONAL**
                  **EXPRESSIONS**.  The words between the **[[** and **]]** do not
                  undergo word splitting and pathname expansion.  The shell
                  performs tilde expansion, parameter and variable expansion,
                  arithmetic expansion, command substitution, process
                  substitution, and quote removal on those words.
                  Conditional operators such as **-f** must be unquoted to be
                  recognized as primaries.
    
                  When used with **[[** , the **< **and **> **operators sort
                  lexicographically using the current locale.
    
                  When the **==** and **!=** operators are used, the string to the
                  right of the operator is considered a pattern and matched
                  according to the rules described below under **Pattern**
                  **Matching** , as if the **extglob** shell option were enabled.  The
                  **=** operator is equivalent to **==**.  If the **nocasematch** shell
                  option is enabled, the match is performed without regard to
                  the case of alphabetic characters.  The return value is 0
                  if the string matches (**==**) or does not match (**!=**) the
                  pattern, and 1 otherwise.  If any part of the pattern is
                  quoted, the quoted portion is matched as a string: every
                  character in the quoted portion matches itself, instead of
                  having any special pattern matching meaning.
    
                  An additional binary operator, **=~** , is available, with the
                  same precedence as **==** and **!=**.  When it is used, the string
                  to the right of the operator is considered a POSIX extended
                  regular expression and matched accordingly (using the POSIX
                  _regcomp_ and _regexec_ interfaces usually described in
                  regex(3)).  The return value is 0 if the string matches the
                  pattern, and 1 otherwise.  If the regular expression is
                  syntactically incorrect, the conditional expression's
                  return value is 2.  If the **nocasematch** shell option is
                  enabled, the match is performed without regard to the case
                  of alphabetic characters.
    
                  If any part of the pattern is quoted, the quoted portion is
                  matched literally, as above.  If the pattern is stored in a
                  shell variable, quoting the variable expansion forces the
                  entire pattern to be matched literally.  Treat bracket
                  expressions in regular expressions carefully, since normal
                  quoting and pattern characters lose their meanings between
                  brackets.
    
                  The match succeeds if the pattern matches any part of the
                  string.  Anchor the pattern using the **^** and **$** regular
                  expression operators to force it to match the entire
                  string.
    
                  The array variable **BASH_REMATCH** records which parts of the
                  string matched the pattern.  The element of **BASH_REMATCH**
                  with index 0 contains the portion of the string matching
                  the entire regular expression.  Substrings matched by
                  parenthesized subexpressions within the regular expression
                  are saved in the remaining **BASH_REMATCH** indices.  The
                  element of **BASH_REMATCH** with index _n_ is the portion of the
                  string matching the _n_ th parenthesized subexpression.  **Bash**
                  sets **BASH_REMATCH** in the global scope; declaring it as a
                  local variable will lead to unexpected results.
    
                  Expressions may be combined using the following operators,
                  listed in decreasing order of precedence:
    
                  **(**_expression_ **)**
                         Returns the value of _expression_.  This may be used
                         to override the normal precedence of operators.
                  **!**_expression_
                         True if _expression_ is false.
                  _expression1_ **& & **_expression2_
                         True if both _expression1_ and _expression2_ are true.
                  _expression1_ **||**_expression2_
                         True if either _expression1_ or _expression2_ is true.
    
                  The **& & **and **||** operators do not evaluate _expression2_ if the
                  value of _expression1_ is sufficient to determine the return
                  value of the entire conditional expression.
    
           **for** _name_ [ [ **in** _word ..._ ] ; ] **do** _list_ ; **done**
                  First, expand The list of words following **in** , generating a
                  list of items.  Then, the variable _name_ is set to each
                  element of this list in turn, and _list_ is executed each
                  time.  If the **in** _word_ is omitted, the **for** command executes
                  _list_ once for each positional parameter that is set (see
                  **PARAMETERS** below).  The return status is the exit status of
                  the last command that executes.  If the expansion of the
                  items following **in** results in an empty list, no commands
                  are executed, and the return status is 0.
    
           **for**(( _expr1_ ; _expr2_ ; _expr3_ )) [;] **do** _list_ ; **done**
                  First, evaluate the arithmetic expression _expr1_ according
                  to the rules described below under **ARITHMETIC EVALUATION**.
                  Then, repeatedly evaluate the arithmetic expression _expr2_
                  until it evaluates to zero.  Each time _expr2_ evaluates to a
                  non-zero value, execute _list_ and evaluate the arithmetic
                  expression _expr3_.  If any expression is omitted, it behaves
                  as if it evaluates to 1.  The return value is the exit
                  status of the last command in _list_ that is executed, or
                  non-zero if any of the expressions is invalid.
    
                  Use the **break** and **continue** builtins (see **SHELL BUILTIN**
                  **COMMANDS** below) to control loop execution.
    
           **select** _name_ [ **in** _word_ ] ; **do** _list_ ; **done**
                  First, expand the list of words following **in** , generating a
                  list of items, and print the set of expanded words the
                  standard error, each preceded by a number.  If the **in** _word_
                  is omitted, print the positional parameters (see **PARAMETERS**
                  below).  **select** then displays the **PS3** prompt and reads a
                  line from the standard input.  If the line consists of a
                  number corresponding to one of the displayed words, then
                  **select** sets the value of _name_ to that word.  If the line is
                  empty, **select** displays the words and prompt again.  If EOF
                  is read, **select** completes and returns 1.  Any other value
                  sets _name_ to null.  The line read is saved in the variable
                  **REPLY**.  The _list_ is executed after each selection until a
                  **break** command is executed.  The exit status of **select** is
                  the exit status of the last command executed in _list_ , or
                  zero if no commands were executed.
    
           **case** _word_ **in**[ [(] _pattern_ [ **|**_pattern_ ] ... ) _list_ ;; ] ... **esac**
                  A **case** command first expands _word_ , and tries to match it
                  against each _pattern_ in turn, proceeding from first to
                  last, using the matching rules described under **Pattern**
                  **Matching** below.  A pattern list is a set of one or more
                  patterns separated by , and the ) operator terminates the
                  pattern list.  The _word_ is expanded using tilde expansion,
                  parameter and variable expansion, arithmetic expansion,
                  command substitution, process substitution and quote
                  removal.  Each _pattern_ examined is expanded using tilde
                  expansion, parameter and variable expansion, arithmetic
                  expansion, command substitution, process substitution, and
                  quote removal.  If the **nocasematch** shell option is enabled,
                  the match is performed without regard to the case of
                  alphabetic characters.  A _clause_ is a pattern list and an
                  associated _list_.
    
                  When a match is found, **case** executes the corresponding
                  _list_.  If the **;;** operator terminates the case clause, the
                  **case** command completes after the first match.  Using **; & **in
                  place of **;;** causes execution to continue with the _list_
                  associated with the next pattern list.  Using **;; & **in place
                  of **;;** causes the shell to test the next pattern list in the
                  statement, if any, and execute any associated _list_ if the
                  match succeeds, continuing the case statement execution as
                  if the pattern list had not matched.  The exit status is
                  zero if no pattern matches.
    
                  Otherwise, it is the exit status of the last command
                  executed in the last _list_ executed.
    
           **if** _list_ ; **then** _list_ ; [ **elif** _list_ ; **then** _list_ ; ] ... [ **else** _list_ ; ]
           **fi**
                  The **if** _list_ is executed.  If its exit status is zero, the
                  **then** _list_ is executed.  Otherwise, each **elif** _list_ is
                  executed in turn, and if its exit status is zero, the
                  corresponding **then** _list_ is executed and the command
                  completes.  Otherwise, the **else** _list_ is executed, if
                  present.  The exit status is the exit status of the last
                  command executed, or zero if no condition tested true.
    
           **while** _list-1_ ; **do** _list-2_ ; **done**
           **until** _list-1_ ; **do** _list-2_ ; **done**
                  The **while** command continuously executes the list _list-2_ as
                  long as the last command in the list _list-1_ returns an exit
                  status of zero.  The **until** command is identical to the
                  **while** command, except that the test is negated: _list-2_ is
                  executed as long as the last command in _list-1_ returns a
                  non-zero exit status.  The exit status of the **while** and
                  **until** commands is the exit status of the last command
                  executed in _list-2_ , or zero if none was executed.
    
       **Coprocesses**
           A _coprocess_ is a shell command preceded by the **coproc** reserved
           word.  A coprocess is executed asynchronously in a subshell, as if
           the command had been terminated with the **& **control operator, with
           a two-way pipe established between the executing shell and the
           coprocess.
    
           The syntax for a coprocess is:
    
                  **coproc**[_NAME_] _command_ [_redirections_]
    
           This creates a coprocess named _NAME_.  _command_ may be either a
           simple command or a compound command (see above).  _NAME_ is a shell
           variable name.  If _NAME_ is not supplied, the default name is
           **COPROC**.
    
           The recommended form to use for a coprocess is
    
                  **coproc** _NAME_ { _command_ [_redirections_]; }
    
           This form is preferred because simple commands result in the
           coprocess always being named **COPROC** , and it is simpler to use and
           more complete than the other compound commands.
    
           If _command_ is a compound command, _NAME_ is optional. The word
           following **coproc** determines whether that word is interpreted as a
           variable name: it is interpreted as _NAME_ if it is not a reserved
           word that introduces a compound command.  If _command_ is a simple
           command, _NAME_ is not allowed; this is to avoid confusion between
           _NAME_ and the first word of the simple command.
    
           When the coprocess is executed, the shell creates an array
           variable (see **Arrays** below) named _NAME_ in the context of the
           executing shell.  The standard output of _command_ is connected via
           a pipe to a file descriptor in the executing shell, and that file
           descriptor is assigned to _NAME_[0].  The standard input of _command_
           is connected via a pipe to a file descriptor in the executing
           shell, and that file descriptor is assigned to _NAME_[1].  This pipe
           is established before any redirections specified by the command
           (see **REDIRECTION** below).  The file descriptors can be utilized as
           arguments to shell commands and redirections using standard word
           expansions.  Other than those created to execute command and
           process substitutions, the file descriptors are not available in
           subshells.
    
           The process ID of the shell spawned to execute the coprocess is
           available as the value of the variable _NAME_ _PID.  The **wait** builtin
           may be used to wait for the coprocess to terminate.
    
           Since the coprocess is created as an asynchronous command, the
           **coproc** command always returns success.  The return status of a
           coprocess is the exit status of _command_.
    
       **Shell Function Definitions**
           A shell function is an object that is called like a simple command
           and executes a compound command with a new set of positional
           parameters.  Shell functions are declared as follows:
    
           _fname_ () _compound-command_ [_redirection_]
           **function** _fname_ [()] _compound-command_ [_redirection_]
                  This defines a function named _fname_.  The reserved word
                  **function** is optional.  If the **function** reserved word is
                  supplied, the parentheses are optional.  The _body_ of the
                  function is the compound command _compound-command_ (see
                  **Compound Commands** above).  That command is usually a _list_
                  of commands between { and }, but may be any command listed
                  under **Compound Commands** above.  If the **function** reserved
                  word is used, but the parentheses are not supplied, the
                  braces are recommended.  _compound-command_ is executed
                  whenever _fname_ is specified as the name of a simple
                  command.  When in posix mode, _fname_ must be a valid shell
                  _name_ and may not be the name of one of the POSIX _special_
                  _builtins_.  In default mode, a function name can be any
                  unquoted shell word that does not contain **$**.
    
           Any redirections (see **REDIRECTION** below) specified when a function
           is defined are performed when the function is executed.
    
           The exit status of a function definition is zero unless a syntax
           error occurs or a readonly function with the same name already
           exists.  When executed, the exit status of a function is the exit
           status of the last command executed in the body.  (See **FUNCTIONS**
           below.)
    


## COMMENTS



           In a non-interactive shell, or an interactive shell in which the
           **interactive_comments** option to the **shopt** builtin is enabled (see
           **SHELL BUILTIN COMMANDS** below), a word beginning with **#** introduces
           a comment.  A word begins at the beginning of a line, after
           unquoted whitespace, or after an operator.  The comment causes
           that word and all remaining characters on that line to be ignored.
           An interactive shell without the **interactive_comments** option
           enabled does not allow comments.  The **interactive_comments** option
           is enabled by default in interactive shells.
    


## QUOTING



           _Quoting_ is used to remove the special meaning of certain
           characters or words to the shell.  Quoting can be used to disable
           special treatment for special characters, to prevent reserved
           words from being recognized as such, and to prevent parameter
           expansion.
    
           Each of the _metacharacters_ listed above under **DEFINITIONS** has
           special meaning to the shell and must be quoted if it is to
           represent itself.
    
           When the command history expansion facilities are being used (see
           **HISTORY EXPANSION** below), the _history expansion_ character, usually
           **!** , must be quoted to prevent history expansion.
    
           There are four quoting mechanisms: the _escape character_ , single
           quotes, double quotes, and dollar-single quotes.
    
           A non-quoted backslash (**\**) is the _escape character_.  It preserves
           the literal value of the next character that follows, removing any
           special meaning it has, with the exception of <newline>.  If a
           **\** <newline> pair appears, and the backslash is not itself quoted,
           the **\** <newline> is treated as a line continuation (that is, it is
           removed from the input stream and effectively ignored).
    
           Enclosing characters in single quotes preserves the literal value
           of each character within the quotes.  A single quote may not occur
           between single quotes, even when preceded by a backslash.
    
           Enclosing characters in double quotes preserves the literal value
           of all characters within the quotes, with the exception of **$** , **`** ,
           **\** , and, when history expansion is enabled, **!**.  When the shell is
           in posix mode, the **!** has no special meaning within double quotes,
           even when history expansion is enabled.  The characters **$** and **`**
           retain their special meaning within double quotes.  The backslash
           retains its special meaning only when followed by one of the
           following characters: **$** , **`** , **"** , **\** , or **< newline>**.  Backslashes
           preceding characters without a special meaning are left
           unmodified.
    
           A double quote may be quoted within double quotes by preceding it
           with a backslash.  If enabled, history expansion will be performed
           unless an **!** appearing in double quotes is escaped using a
           backslash.  The backslash preceding the **!** is not removed.
    
           The special parameters ***** and **@** have special meaning when in double
           quotes (see **PARAMETERS** below).
    
           Character sequences of the form **$** '_string_ ' are treated as a special
           variant of single quotes.  The sequence expands to _string_ , with
           backslash-escaped characters in _string_ replaced as specified by
           the ANSI C standard.  Backslash escape sequences, if present, are
           decoded as follows:
                  **\a** alert (bell)
                  **\b** backspace
                  **\e**
                  **\E** an escape character
                  **\f** form feed
                  **\n** new line
                  **\r** carriage return
                  **\t** horizontal tab
                  **\v** vertical tab
                  **\\** backslash
                  **\'** single quote
                  **\"** double quote
                  **\?** question mark
                  **\**_nnn_   The eight-bit character whose value is the octal
                         value _nnn_ (one to three octal digits).
                  **\x** _HH_   The eight-bit character whose value is the
                         hexadecimal value _HH_ (one or two hex digits).
                  **\u** _HHHH_ The Unicode (ISO/IEC 10646) character whose value is
                         the hexadecimal value _HHHH_ (one to four hex digits).
                  **\U** _HHHHHHHH_
                         The Unicode (ISO/IEC 10646) character whose value is
                         the hexadecimal value _HHHHHHHH_ (one to eight hex
                         digits).
                  **\c** _x_    A control-_x_ character.
    
           The expanded result is single-quoted, as if the dollar sign had
           not been present.
    
       **Translating Strings**
           A double-quoted string preceded by a dollar sign (**$** "_string_ ")
           causes the string to be translated according to the current
           locale.  The _gettext_ infrastructure performs the lookup and
           translation, using the **LC_MESSAGES** , **TEXTDOMAINDIR** , and **TEXTDOMAIN**
           shell variables.  If the current locale is **C** or **POSIX** , if there
           are no translations available, or if the string is not translated,
           the dollar sign is ignored, and the string is treated as double-
           quoted as described above.  This is a form of double quoting, so
           the string remains double-quoted by default, whether or not it is
           translated and replaced.  If the **noexpand_translation** option is
           enabled using the **shopt** builtin, translated strings are single-
           quoted instead of double-quoted.  See the description of **shopt**
           below under **SHELL BUILTIN COMMANDS**.
    


## PARAMETERS



           A _parameter_ is an entity that stores values.  It can be a _name_ , a
           number, or one of the special characters listed below under
           **Special Parameters**.  A _variable_ is a parameter denoted by a _name_.
           A variable has a _value_ and zero or more _attributes_.  Attributes
           are assigned using the **declare** builtin command (see **declare** below
           in **SHELL BUILTIN COMMANDS**).  The **export** and **readonly** builtins
           assign specific attributes.
    
           A parameter is set if it has been assigned a value.  The null
           string is a valid value.  Once a variable is set, it may be unset
           only by using the **unset** builtin command (see **SHELL BUILTIN**
           **COMMANDS** below).
    
           A _variable_ is assigned to using a statement of the form
    
                  _name_ =[_value_]
    
           If _value_ is not given, the variable is assigned the null string.
           All _values_ undergo tilde expansion, parameter and variable
           expansion, command substitution, arithmetic expansion, and quote
           removal (see **EXPANSION** below).  If the variable has its **integer**
           attribute set, then _value_ is evaluated as an arithmetic expression
           even if the **$((**...**))** expansion is not used (see **Arithmetic**
           **Expansion** below).  Word splitting and pathname expansion are not
           performed.  Assignment statements may also appear as arguments to
           the **alias** , **declare** , **typeset** , **export** , **readonly** , and **local** builtin
           commands (_declaration_ commands).  When in posix mode, these
           builtins may appear in a command after one or more instances of
           the **command** builtin and retain these assignment statement
           properties.
    
           In the context where an assignment statement is assigning a value
           to a shell variable or array index, the “+=” operator appends to
           or adds to the variable's previous value.  This includes arguments
           to _declaration_ commands such as **declare** that accept assignment
           statements.  When “+=” is applied to a variable for which the
           **integer** attribute has been set, the variable's current value and
           _value_ are each evaluated as arithmetic expressions, and the sum of
           the results is assigned as the variable's value.  The current
           value is usually an integer constant, but may be an expression.
           When “+=” is applied to an array variable using compound
           assignment (see **Arrays** below), the variable's value is not unset
           (as it is when using “=”), and new values are appended to the
           array beginning at one greater than the array's maximum index (for
           indexed arrays) or added as additional key-value pairs in an
           associative array.  When applied to a string-valued variable,
           _value_ is expanded and appended to the variable's value.
    
           A variable can be assigned the _nameref_ attribute using the **-n**
           option to the **declare** or **local** builtin commands (see the
           descriptions of **declare** and **local** below) to create a _nameref_ , or a
           reference to another variable.  This allows variables to be
           manipulated indirectly.  Whenever the nameref variable is
           referenced, assigned to, unset, or has its attributes modified
           (other than using or changing the _nameref_ attribute itself), the
           operation is actually performed on the variable specified by the
           nameref variable's value.  A nameref is commonly used within shell
           functions to refer to a variable whose name is passed as an
           argument to the function.  For instance, if a variable name is
           passed to a shell function as its first argument, running
    
                  declare -n ref=$1
    
           inside the function creates a local nameref variable **ref** whose
           value is the variable name passed as the first argument.
           References and assignments to **ref** , and changes to its attributes,
           are treated as references, assignments, and attribute
           modifications to the variable whose name was passed as **$1**.  If the
           control variable in a **for** loop has the nameref attribute, the list
           of words can be a list of shell variables, and a name reference is
           established for each word in the list, in turn, when the loop is
           executed.  Array variables cannot be given the **nameref** attribute.
           However, nameref variables can reference array variables and
           subscripted array variables.  Namerefs can be unset using the **-n**
           option to the **unset** builtin.  Otherwise, if **unset** is executed with
           the name of a nameref variable as an argument, the variable
           referenced by the nameref variable is unset.
    
           When the shell starts, it reads its environment and creates a
           shell variable from each environment variable that has a valid
           name, as described below (see **ENVIRONMENT**).
    
       **Positional Parameters**
           A _positional parameter_ is a parameter denoted by one or more
           digits, other than the single digit 0.  Positional parameters are
           assigned from the shell's arguments when it is invoked, and may be
           reassigned using the **set** builtin command.  Positional parameters
           may not be assigned to with assignment statements.  The positional
           parameters are temporarily replaced when a shell function is
           executed (see **FUNCTIONS** below).
    
           When a positional parameter consisting of more than a single digit
           is expanded, it must be enclosed in braces (see **EXPANSION** below).
           Without braces, a digit following $ can only refer to one of the
           first nine positional parameters (**$1-$9**) or the special parameter
           **$0**(see the next section).
    
       **Special Parameters**
           The shell treats several parameters specially.  These parameters
           may only be referenced; assignment to them is not allowed.
           Special parameters are denoted by one of the following characters.
    
           *****(**$***) Expands to the positional parameters, starting from
                  one.  When the expansion is not within double quotes, each
                  positional parameter expands to a separate word.  In
                  contexts where word expansions are performed, those words
                  are subject to further word splitting and pathname
                  expansion.  When the expansion occurs within double quotes,
                  it expands to a single word with the value of each
                  parameter separated by the first character of the **IFS**
                  variable.  That is, **"$*"** is equivalent to **"$1** _c_**$2** _c_**..."** ,
                  where _c_ is the first character of the value of the **IFS**
                  variable.  If **IFS** is unset, the parameters are separated by
                  spaces.  If **IFS** is null, the parameters are joined without
                  intervening separators.
           **@**(**$@**) Expands to the positional parameters, starting from
                  one.  In contexts where word splitting is performed, this
                  expands each positional parameter to a separate word; if
                  not within double quotes, these words are subject to word
                  splitting.  In contexts where word splitting is not
                  performed, such as the value portion of an assignment
                  statement, this expands to a single word with each
                  positional parameter separated by a space.  When the
                  expansion occurs within double quotes, and word splitting
                  is performed, each parameter expands to a separate word.
                  That is, **"$@"** is equivalent to **"$1" "$2" ...** If the
                  double-quoted expansion occurs within a word, the expansion
                  of the first parameter is joined with the expansion of the
                  beginning part of the original word, and the expansion of
                  the last parameter is joined with the expansion of the last
                  part of the original word.  When there are no positional
                  parameters, **"$@"** and **$@** expand to nothing (i.e., they are
                  removed).
           **#**(**$#**) Expands to the number of positional parameters in
                  decimal.
           **?**(**$?**) Expands to the exit status of the most recently
                  executed command.
           **-**(**$-**) Expands to the current option flags as specified upon
                  invocation, by the **set** builtin command, or those set by the
                  shell itself (such as the **-i** option).
           **$**(**$$**) Expands to the process ID of the shell.  In a
                  subshell, it expands to the process ID of the parent shell,
                  not the subshell.
           **!**(**$!**)Expands to the process ID of the job most recently
                  placed into the background, whether executed as an
                  asynchronous command or using the **bg** builtin (see **JOB**
                  **CONTROL** below).
           **0**(**$0**) Expands to the name of the shell or shell script.
                  This is set at shell initialization.  If **bash** is invoked
                  with a file of commands, **$0** is set to the name of that
                  file.  If **bash** is started with the **-c** option, then **$0** is
                  set to the first argument after the string to be executed,
                  if one is present.  Otherwise, it is set to the filename
                  used to invoke **bash** , as given by argument zero.
    
       **Shell Variables**
           The shell sets following variables:
    
           **_**(**$_** , an underscore) This has a number of meanings depending
                  on context.  At shell startup, **_** is set to the pathname
                  used to invoke the shell or shell script being executed as
                  passed in the environment or argument list.  Subsequently,
                  it expands to the last argument to the previous simple
                  command executed in the foreground, after expansion.  It is
                  also set to the full pathname used to invoke each command
                  executed and placed in the environment exported to that
                  command.  When checking mail, **$_** expands to the name of the
                  mail file currently being checked.
           **BASH** Expands to the full filename used to invoke this instance
                  of **bash**.
           **BASHOPTS**
                  A colon-separated list of enabled shell options.  Each word
                  in the list is a valid argument for the **-s** option to the
                  **shopt** builtin command (see **SHELL BUILTIN COMMANDS** below).
                  The options appearing in **BASHOPTS** are those reported as _on_
                  by **shopt**.  If this variable is in the environment when **bash**
                  starts up, the shell enables each option in the list before
                  reading any startup files.  If this variable is exported,
                  child shells will enable each option in the list.  This
                  variable is read-only.
           **BASHPID**
                  Expands to the process ID of the current **bash** process.
                  This differs from **$$** under certain circumstances, such as
                  subshells that do not require **bash** to be re-initialized.
                  Assignments to **BASHPID** have no effect.  If **BASHPID** is
                  unset, it loses its special properties, even if it is
                  subsequently reset.
           **BASH_ALIASES**
                  An associative array variable whose members correspond to
                  the internal list of aliases as maintained by the **alias**
                  builtin.  Elements added to this array appear in the alias
                  list; however, unsetting array elements currently does not
                  remove aliases from the alias list.  If **BASH_ALIASES** is
                  unset, it loses its special properties, even if it is
                  subsequently reset.
           **BASH_ARGC**
                  An array variable whose values are the number of parameters
                  in each frame of the current **bash** execution call stack.
                  The number of parameters to the current subroutine (shell
                  function or script executed with **.** or **source**) is at the top
                  of the stack.  When a subroutine is executed, the number of
                  parameters passed is pushed onto **BASH_ARGC**.  The shell sets
                  **BASH_ARGC** only when in extended debugging mode (see the
                  description of the **extdebug** option to the **shopt** builtin
                  below).  Setting **extdebug** after the shell has started to
                  execute a script, or referencing this variable when
                  **extdebug** is not set, may result in inconsistent values.
                  Assignments to **BASH_ARGC** have no effect, and it may not be
                  unset.
           **BASH_ARGV**
                  An array variable containing all of the parameters in the
                  current **bash** execution call stack.  The final parameter of
                  the last subroutine call is at the top of the stack; the
                  first parameter of the initial call is at the bottom.  When
                  a subroutine is executed, the shell pushes the supplied
                  parameters onto **BASH_ARGV**.  The shell sets **BASH_ARGV** only
                  when in extended debugging mode (see the description of the
                  **extdebug** option to the **shopt** builtin below).  Setting
                  **extdebug** after the shell has started to execute a script,
                  or referencing this variable when **extdebug** is not set, may
                  result in inconsistent values.  Assignments to **BASH_ARGV**
                  have no effect, and it may not be unset.
           **BASH_ARGV0**
                  When referenced, this variable expands to the name of the
                  shell or shell script (identical to **$0** ; see the description
                  of special parameter 0 above).  Assigning a value to
                  **BASH_ARGV0** sets **$0** to the same value.  If **BASH_ARGV0** is
                  unset, it loses its special properties, even if it is
                  subsequently reset.
           **BASH_CMDS**
                  An associative array variable whose members correspond to
                  the internal hash table of commands as maintained by the
                  **hash** builtin.  Adding elements to this array makes them
                  appear in the hash table; however, unsetting array elements
                  currently does not remove command names from the hash
                  table.  If **BASH_CMDS** is unset, it loses its special
                  properties, even if it is subsequently reset.
           **BASH_COMMAND**
                  Expands to the command currently being executed or about to
                  be executed, unless the shell is executing a command as the
                  result of a trap, in which case it is the command executing
                  at the time of the trap.  If **BASH_COMMAND** is unset, it
                  loses its special properties, even if it is subsequently
                  reset.
           **BASH_EXECUTION_STRING**
                  The command argument to the **-c** invocation option.
           **BASH_LINENO**
                  An array variable whose members are the line numbers in
                  source files where each corresponding member of **FUNCNAME**
                  was invoked.  **${BASH_LINENO[**_$i_**]}** is the line number in the
                  source file (**${BASH_SOURCE[**_$i+1_**]}**) where **${FUNCNAME[**_$i_**]}**
                  was called (or **${BASH_LINENO[**_$i-1_**]}** if referenced within
                  another shell function).  Use **LINENO** to obtain the current
                  line number.  Assignments to **BASH_LINENO** have no effect,
                  and it may not be unset.
           **BASH_LOADABLES_PATH**
                  A colon-separated list of directories in which the **enable**
                  command looks for dynamically loadable builtins.
           **BASH_MONOSECONDS**
                  Each time this variable is referenced, it expands to the
                  value returned by the system's monotonic clock, if one is
                  available.  If there is no monotonic clock, this is
                  equivalent to **EPOCHSECONDS**.  If **BASH_MONOSECONDS** is unset,
                  it loses its special properties, even if it is subsequently
                  reset.
           **BASH_REMATCH**
                  An array variable whose members are assigned by the **=~**
                  binary operator to the **[[** conditional command.  The element
                  with index 0 is the portion of the string matching the
                  entire regular expression.  The element with index _n_ is the
                  portion of the string matching the _n_ th parenthesized
                  subexpression.
           **BASH_SOURCE**
                  An array variable whose members are the source filenames
                  where the corresponding shell function names in the
                  **FUNCNAME** array variable are defined.  The shell function
                  **${FUNCNAME[**_$i_**]}** is defined in the file **${BASH_SOURCE[**_$i_**]}**
                  and called from **${BASH_SOURCE[**_$i+1_**]}**.  Assignments to
                  **BASH_SOURCE** have no effect, and it may not be unset.
           **BASH_SUBSHELL**
                  Incremented by one within each subshell or subshell
                  environment when the shell begins executing in that
                  environment.  The initial value is 0.  If **BASH_SUBSHELL** is
                  unset, it loses its special properties, even if it is
                  subsequently reset.
           **BASH_TRAPSIG**
                  Set to the signal number corresponding to the trap action
                  being executed during its execution.  See the description
                  of **trap** under **SHELL BUILTIN COMMANDS** below for information
                  about signal numbers and trap execution.
           **BASH_VERSINFO**
                  A readonly array variable whose members hold version
                  information for this instance of **bash**.  The values assigned
                  to the array members are as follows:
                  **BASH_VERSINFO[** 0**]**
                         The major version number (the _release_).
                  **BASH_VERSINFO[** 1**]**
                         The minor version number (the _version_).
                  **BASH_VERSINFO[** 2**]**
                         The patch level.
                  **BASH_VERSINFO[** 3**]**
                         The build version.
                  **BASH_VERSINFO[** 4**]**
                         The release status (e.g., _beta_).
                  **BASH_VERSINFO[** 5**]**
                         The value of **MACHTYPE**.
           **BASH_VERSION**
                  Expands to a string describing the version of this instance
                  of **bash**(e.g., 5.2.37(3)-release).
           **COMP_CWORD**
                  An index into **${COMP_WORDS}** of the word containing the
                  current cursor position.  This variable is available only
                  in shell functions invoked by the programmable completion
                  facilities (see **Programmable Completion** below).
           **COMP_KEY**
                  The key (or final key of a key sequence) used to invoke the
                  current completion function.  This variable is available
                  only in shell functions and external commands invoked by
                  the programmable completion facilities (see **Programmable**
                  **Completion** below).
           **COMP_LINE**
                  The current command line.  This variable is available only
                  in shell functions and external commands invoked by the
                  programmable completion facilities (see **Programmable**
                  **Completion** below).
           **COMP_POINT**
                  The index of the current cursor position relative to the
                  beginning of the current command.  If the current cursor
                  position is at the end of the current command, the value of
                  this variable is equal to **${#COMP_LINE}**.  This variable is
                  available only in shell functions and external commands
                  invoked by the programmable completion facilities (see
                  **Programmable Completion** below).
           **COMP_TYPE**
                  Set to an integer value corresponding to the type of
                  attempted completion that caused a completion function to
                  be called: _TAB_ , for normal completion, _?_ , for listing
                  completions after successive tabs, _!_ , for listing
                  alternatives on partial word completion, _@_ , to list
                  completions if the word is not unmodified, or _%_ , for menu
                  completion.  This variable is available only in shell
                  functions and external commands invoked by the programmable
                  completion facilities (see **Programmable Completion** below).
           **COMP_WORDBREAKS**
                  The set of characters that the **readline** library treats as
                  word separators when performing word completion.  If
                  **COMP_WORDBREAKS** is unset, it loses its special properties,
                  even if it is subsequently reset.
           **COMP_WORDS**
                  An array variable (see **Arrays** below) consisting of the
                  individual words in the current command line.  The line is
                  split into words as **readline** would split it, using
                  **COMP_WORDBREAKS** as described above.  This variable is
                  available only in shell functions invoked by the
                  programmable completion facilities (see **Programmable**
                  **Completion** below).
           **COPROC** An array variable (see **Arrays** below) created to hold the
                  file descriptors for output from and input to an unnamed
                  coprocess (see **Coprocesses** above).
           **DIRSTACK**
                  An array variable (see **Arrays** below) containing the current
                  contents of the directory stack.  Directories appear in the
                  stack in the order they are displayed by the **dirs** builtin.
                  Assigning to members of this array variable may be used to
                  modify directories already in the stack, but the **pushd** and
                  **popd** builtins must be used to add and remove directories.
                  Assigning to this variable does not change the current
                  directory.  If **DIRSTACK** is unset, it loses its special
                  properties, even if it is subsequently reset.
           **EPOCHREALTIME**
                  Each time this parameter is referenced, it expands to the
                  number of seconds since the Unix Epoch (see **time**(3)) as a
                  floating-point value with micro-second granularity.
                  Assignments to **EPOCHREALTIME** are ignored.  If **EPOCHREALTIME**
                  is unset, it loses its special properties, even if it is
                  subsequently reset.
           **EPOCHSECONDS**
                  Each time this parameter is referenced, it expands to the
                  number of seconds since the Unix Epoch (see **time**(3)).
                  Assignments to **EPOCHSECONDS** are ignored.  If **EPOCHSECONDS**
                  is unset, it loses its special properties, even if it is
                  subsequently reset.
           **EUID** Expands to the effective user ID of the current user,
                  initialized at shell startup.  This variable is readonly.
           **FUNCNAME**
                  An array variable containing the names of all shell
                  functions currently in the execution call stack.  The
                  element with index 0 is the name of any currently-executing
                  shell function.  The bottom-most element (the one with the
                  highest index) is “main”.  This variable exists only when a
                  shell function is executing.  Assignments to **FUNCNAME** have
                  no effect.  If **FUNCNAME** is unset, it loses its special
                  properties, even if it is subsequently reset.
    
                  This variable can be used with **BASH_LINENO** and **BASH_SOURCE**.
                  Each element of **FUNCNAME** has corresponding elements in
                  **BASH_LINENO** and **BASH_SOURCE** to describe the call stack.
                  For instance, **${FUNCNAME[**_$i_**]}** was called from the file
                  **${BASH_SOURCE[**_$i+1_**]}** at line number **${BASH_LINENO[**_$i_**]}**.
                  The **caller** builtin displays the current call stack using
                  this information.
           **GROUPS** An array variable containing the list of groups of which
                  the current user is a member.  Assignments to **GROUPS** have
                  no effect.  If **GROUPS** is unset, it loses its special
                  properties, even if it is subsequently reset.
           **HISTCMD**
                  The history number, or index in the history list, of the
                  current command.  Assignments to **HISTCMD** have no effect.
                  If **HISTCMD** is unset, it loses its special properties, even
                  if it is subsequently reset.
           **HOSTNAME**
                  Automatically set to the name of the current host.
           **HOSTTYPE**
                  Automatically set to a string that uniquely describes the
                  type of machine on which **bash** is executing.  The default is
                  system-dependent.
           **LINENO** Each time this parameter is referenced, the shell
                  substitutes a decimal number representing the current
                  sequential line number (starting with 1) within a script or
                  function.  When not in a script or function, the value
                  substituted is not guaranteed to be meaningful.  If **LINENO**
                  is unset, it loses its special properties, even if it is
                  subsequently reset.
           **MACHTYPE**
                  Automatically set to a string that fully describes the
                  system type on which **bash** is executing, in the standard GNU
                  _cpu-company-system_ format.  The default is system-
                  dependent.
           **MAPFILE**
                  An array variable (see **Arrays** below) created to hold the
                  text read by the **mapfile** builtin when no variable name is
                  supplied.
           **OLDPWD** The previous working directory as set by the **cd** command.
           **OPTARG** The value of the last option argument processed by the
                  **getopts** builtin command (see **SHELL BUILTIN COMMANDS** below).
           **OPTIND** The index of the next argument to be processed by the
                  **getopts** builtin command (see **SHELL BUILTIN COMMANDS** below).
           **OSTYPE** Automatically set to a string that describes the operating
                  system on which **bash** is executing.  The default is system-
                  dependent.
           **PIPESTATUS**
                  An array variable (see **Arrays** below) containing a list of
                  exit status values from the commands in the most-recently-
                  executed foreground pipeline, which may consist of only a
                  simple command (see **SHELL GRAMMAR** above).  **Bash** sets
                  **PIPESTATUS** after executing multi-element pipelines, timed
                  and negated pipelines, simple commands, subshells created
                  with the ( operator, the **[[** and **((** compound commands, and
                  after error conditions that result in the shell aborting
                  command execution.
           **PPID** The process ID of the shell's parent.  This variable is
                  readonly.
           **PWD** The current working directory as set by the **cd** command.
           **RANDOM** Each time this parameter is referenced, it expands to a
                  random integer between 0 and 32767.  Assigning a value to
                  **RANDOM** initializes (seeds) the sequence of random numbers.
                  Seeding the random number generator with the same constant
                  value produces the same sequence of values.  If **RANDOM** is
                  unset, it loses its special properties, even if it is
                  subsequently reset.
           **READLINE_ARGUMENT**
                  Any numeric argument given to a **readline** command that was
                  defined using “bind -x” (see **SHELL BUILTIN COMMANDS** below)
                  when it was invoked.
           **READLINE_LINE**
                  The contents of the **readline** line buffer, for use with
                  “bind -x” (see **SHELL BUILTIN COMMANDS** below).
           **READLINE_MARK**
                  The position of the mark (saved insertion point) in the
                  **readline** line buffer, for use with “bind -x” (see **SHELL**
                  **BUILTIN COMMANDS** below).  The characters between the
                  insertion point and the mark are often called the _region_.
           **READLINE_POINT**
                  The position of the insertion point in the **readline** line
                  buffer, for use with “bind -x” (see **SHELL BUILTIN COMMANDS**
                  below).
           **REPLY** Set to the line of input read by the **read** builtin command
                  when no arguments are supplied.
           **SECONDS**
                  Each time this parameter is referenced, it expands to the
                  number of seconds since shell invocation.  If a value is
                  assigned to **SECONDS** , the value returned upon subsequent
                  references is the number of seconds since the assignment
                  plus the value assigned.  The number of seconds at shell
                  invocation and the current time are always determined by
                  querying the system clock at one-second resolution.  If
                  **SECONDS** is unset, it loses its special properties, even if
                  it is subsequently reset.
           **SHELLOPTS**
                  A colon-separated list of enabled shell options.  Each word
                  in the list is a valid argument for the **-o** option to the
                  **set** builtin command (see **SHELL BUILTIN COMMANDS** below).
                  The options appearing in **SHELLOPTS** are those reported as _on_
                  by **set -o**.  If this variable is in the environment when
                  **bash** starts up, the shell enables each option in the list
                  before reading any startup files.  If this variable is
                  exported, child shells will enable each option in the list.
                  This variable is read-only.
           **SHLVL** Incremented by one each time an instance of **bash** is
                  started.
           **SRANDOM**
                  Each time it is referenced, this variable expands to a
                  32-bit pseudo-random number.  The random number generator
                  is not linear on systems that support _/dev/urandom_ or
                  arc4random(3), so each returned number has no relationship
                  to the numbers preceding it.  The random number generator
                  cannot be seeded, so assignments to this variable have no
                  effect.  If **SRANDOM** is unset, it loses its special
                  properties, even if it is subsequently reset.
           **UID** Expands to the user ID of the current user, initialized at
                  shell startup.  This variable is readonly.
    
           The shell uses the following variables. In some cases, **bash**
           assigns a default value to a variable; these cases are noted
           below.
    
           **BASH_COMPAT**
                  The value is used to set the shell's compatibility level.
                  See **SHELL COMPATIBILITY MODE** below for a description of the
                  various compatibility levels and their effects.  The value
                  may be a decimal number (e.g., 4.2) or an integer (e.g.,
                  42) corresponding to the desired compatibility level.  If
                  **BASH_COMPAT** is unset or set to the empty string, the
                  compatibility level is set to the default for the current
                  version.  If **BASH_COMPAT** is set to a value that is not one
                  of the valid compatibility levels, the shell prints an
                  error message and sets the compatibility level to the
                  default for the current version.  A subset of the valid
                  values correspond to the compatibility levels described
                  below under **SHELL COMPATIBILITY MODE**.  For example, 4.2 and
                  42 are valid values that correspond to the **compat42 shopt**
                  option and set the compatibility level to 42.  The current
                  version is also a valid value.
           **BASH_ENV**
                  If this parameter is set when **bash** is executing a shell
                  script, its expanded value is interpreted as a filename
                  containing commands to initialize the shell before it reads
                  and executes commands from the script.  The value of
                  **BASH_ENV** is subjected to parameter expansion, command
                  substitution, and arithmetic expansion before being
                  interpreted as a filename.  **PATH** is not used to search for
                  the resultant filename.
           **BASH_XTRACEFD**
                  If set to an integer corresponding to a valid file
                  descriptor, **bash** writes the trace output generated when
                  “set -x” is enabled to that file descriptor, instead of the
                  standard error.  The file descriptor is closed when
                  **BASH_XTRACEFD** is unset or assigned a new value.  Unsetting
                  **BASH_XTRACEFD** or assigning it the empty string causes the
                  trace output to be sent to the standard error.  Note that
                  setting **BASH_XTRACEFD** to 2 (the standard error file
                  descriptor) and then unsetting it will result in the
                  standard error being closed.
           **CDPATH** The search path for the **cd** command.  This is a colon-
                  separated list of directories where the shell looks for
                  directories specified as arguments to the **cd** command.  A
                  sample value is “.:~:/usr”.
           **CHILD_MAX**
                  Set the number of exited child status values for the shell
                  to remember.  **Bash** will not allow this value to be
                  decreased below a POSIX-mandated minimum, and there is a
                  maximum value (currently 8192) that this may not exceed.
                  The minimum value is system-dependent.
           **COLUMNS**
                  Used by the **select** compound command to determine the
                  terminal width when printing selection lists.
                  Automatically set if the **checkwinsize** option is enabled or
                  in an interactive shell upon receipt of a **SIGWINCH**.
           **COMPREPLY**
                  An array variable from which **bash** reads the possible
                  completions generated by a shell function invoked by the
                  programmable completion facility (see **Programmable**
                  **Completion** below).  Each array element contains one
                  possible completion.
           **EMACS** If **bash** finds this variable in the environment when the
                  shell starts with value “t”, it assumes that the shell is
                  running in an Emacs shell buffer and disables line editing.
           **ENV** Expanded and executed similarly to **BASH_ENV**(see **INVOCATION**
                  above) when an interactive shell is invoked in posix mode.
           **EXECIGNORE**
                  A colon-separated list of shell patterns (see **Pattern**
                  **Matching**) defining the set of filenames to be ignored by
                  command search using **PATH**.  Files whose full pathnames
                  match one of these patterns are not considered executable
                  files for the purposes of completion and command execution
                  via **PATH** lookup.  This does not affect the behavior of the
                  **[** , **test** , and **[[** commands.  Full pathnames in the command
                  hash table are not subject to **EXECIGNORE**.  Use this
                  variable to ignore shared library files that have the
                  executable bit set, but are not executable files.  The
                  pattern matching honors the setting of the **extglob** shell
                  option.
           **FCEDIT** The default editor for the **fc** builtin command.
           **FIGNORE**
                  A colon-separated list of suffixes to ignore when
                  performing filename completion (see **READLINE** below).  A
                  filename whose suffix matches one of the entries in **FIGNORE**
                  is excluded from the list of matched filenames.  A sample
                  value is “.o:~”.
           **FUNCNEST**
                  If set to a numeric value greater than 0, defines a maximum
                  function nesting level.  Function invocations that exceed
                  this nesting level cause the current command to abort.
           **GLOBIGNORE**
                  A colon-separated list of patterns defining the set of file
                  names to be ignored by pathname expansion.  If a file name
                  matched by a pathname expansion pattern also matches one of
                  the patterns in **GLOBIGNORE** , it is removed from the list of
                  matches.  The pattern matching honors the setting of the
                  **extglob** shell option.
           **GLOBSORT**
                  Controls how the results of pathname expansion are sorted.
                  The value of this variable specifies the sort criteria and
                  sort order for the results of pathname expansion.  If this
                  variable is unset or set to the null string, pathname
                  expansion uses the historical behavior of sorting by name,
                  in ascending lexicographic order as determined by the
                  **LC_COLLATE** shell variable.
    
                  If set, a valid value begins with an optional _+_ , which is
                  ignored, or _-_ , which reverses the sort order from ascending
                  to descending, followed by a sort specifier.  The valid
                  sort specifiers are _name_ , _numeric_ , _size_ , _mtime_ , _atime_ ,
                  _ctime_ , and _blocks_ , which sort the files on name, names in
                  numeric rather than lexicographic order, file size,
                  modification time, access time, inode change time, and
                  number of blocks, respectively.  If any of the non-name
                  keys compare as equal (e.g., if two files are the same
                  size), sorting uses the name as a secondary sort key.
    
                  For example, a value of _-mtime_ sorts the results in
                  descending order by modification time (newest first).
    
                  The _numeric_ specifier treats names consisting solely of
                  digits as numbers and sorts them using their numeric value
                  (so “2” sorts before “10”, for example).  When using
                  _numeric_ , names containing non-digits sort after all the
                  all-digit names and are sorted by name using the
                  traditional behavior.
    
                  A sort specifier of _nosort_ disables sorting completely;
                  **bash** returns the results in the order they are read from
                  the file system, ignoring any leading _-_.
    
                  If the sort specifier is missing, it defaults to _name_ , so a
                  value of _+_ is equivalent to the null string, and a value of
                  _-_ sorts by name in descending order.  Any invalid value
                  restores the historical sorting behavior.
           **HISTCONTROL**
                  A colon-separated list of values controlling how commands
                  are saved on the history list.  If the list of values
                  includes _ignorespace_ , lines which begin with a **space**
                  character are not saved in the history list.  A value of
                  _ignoredups_ causes lines matching the previous history entry
                  not to be saved.  A value of _ignoreboth_ is shorthand for
                  _ignorespace_ and _ignoredups_.  A value of _erasedups_ causes
                  all previous lines matching the current line to be removed
                  from the history list before that line is saved.  Any value
                  not in the above list is ignored.  If **HISTCONTROL** is unset,
                  or does not include a valid value, **bash** saves all lines
                  read by the shell parser on the history list, subject to
                  the value of **HISTIGNORE**.  If the first line of a multi-line
                  compound command was saved, the second and subsequent lines
                  are not tested, and are added to the history regardless of
                  the value of **HISTCONTROL**.  If the first line was not saved,
                  the second and subsequent lines of the command are not
                  saved either.
           **HISTFILE**
                  The name of the file in which command history is saved (see
                  **HISTORY** below).  **Bash** assigns a default value of
                  _~/.bash_history_.  If **HISTFILE** is unset or null, the shell
                  does not save the command history when it exits.
           **HISTFILESIZE**
                  The maximum number of lines contained in the history file.
                  When this variable is assigned a value, the history file is
                  truncated, if necessary, to contain no more than the number
                  of history entries that total no more than that number of
                  lines by removing the oldest entries.  If the history list
                  contains multi-line entries, the history file may contain
                  more lines than this maximum to avoid leaving partial
                  history entries.  The history file is also truncated to
                  this size after writing it when a shell exits or by the
                  **history** builtin.  If the value is 0, the history file is
                  truncated to zero size.  Non-numeric values and numeric
                  values less than zero inhibit truncation.  The shell sets
                  the default value to the value of **HISTSIZE** after reading
                  any startup files.
           **HISTIGNORE**
                  A colon-separated list of patterns used to decide which
                  command lines should be saved on the history list.  If a
                  command line matches one of the patterns in the value of
                  **HISTIGNORE** , it is not saved on the history list.  Each
                  pattern is anchored at the beginning of the line and must
                  match the complete line (**bash** does not  implicitly append a
                  “***** ”).  Each pattern is tested against the line after the
                  checks specified by **HISTCONTROL** are applied.  In addition
                  to the normal shell pattern matching characters, “**&** ”
                  matches the previous history line.  A backslash escapes the
                  “**&** ”; the backslash is removed before attempting a match.
                  If the first line of a multi-line compound command was
                  saved, the second and subsequent lines are not tested, and
                  are added to the history regardless of the value of
                  **HISTIGNORE**.  If the first line was not saved, the second
                  and subsequent lines of the command are not saved either.
                  The pattern matching honors the setting of the **extglob**
                  shell option.
                  **HISTIGNORE** subsumes some of the function of **HISTCONTROL**.  A
                  pattern of “&” is identical to “ignoredups”, and a pattern
                  of “[ ]*” is identical to “ignorespace”.  Combining these
                  two patterns, separating them with a colon, provides the
                  functionality of “ignoreboth”.
           **HISTSIZE**
                  The number of commands to remember in the command history
                  (see **HISTORY** below).  If the value is 0, commands are not
                  saved in the history list.  Numeric values less than zero
                  result in every command being saved on the history list
                  (there is no limit).  The shell sets the default value to
                  500 after reading any startup files.
           **HISTTIMEFORMAT**
                  If this variable is set and not null, its value is used as
                  a format string for strftime(3) to print the time stamp
                  associated with each history entry displayed by the **history**
                  builtin.  If this variable is set, the shell writes time
                  stamps to the history file so they may be preserved across
                  shell sessions.  This uses the history comment character to
                  distinguish timestamps from other history lines.
           **HOME** The home directory of the current user; the default
                  argument for the **cd** builtin command.  The value of this
                  variable is also used when performing tilde expansion.
           **HOSTFILE**
                  Contains the name of a file in the same format as
                  _/etc/hosts_ that should be read when the shell needs to
                  complete a hostname.  The list of possible hostname
                  completions may be changed while the shell is running; the
                  next time hostname completion is attempted after the value
                  is changed, **bash** adds the contents of the new file to the
                  existing list.  If **HOSTFILE** is set, but has no value, or
                  does not name a readable file, **bash** attempts to read
                  _/etc/hosts_ to obtain the list of possible hostname
                  completions.  When **HOSTFILE** is unset, **bash** clears the
                  hostname list.
           **IFS** The _Internal Field Separator_ that is used for word
                  splitting after expansion and to split lines into words
                  with the **read** builtin command.  Word splitting is described
                  below under **EXPANSION**.  The default value is
                  “<space><tab><newline>”.
           **IGNOREEOF**
                  Controls the action of an interactive shell on receipt of
                  an **EOF** character as the sole input.  If set, the value is
                  the number of consecutive **EOF** characters which must be
                  typed as the first characters on an input line before **bash**
                  exits.  If the variable is set but does not have a numeric
                  value, or the value is null, the default value is 10.  If
                  it is unset, **EOF** signifies the end of input to the shell.
           **INPUTRC**
                  The filename for the **readline** startup file, overriding the
                  default of _~/.inputrc_ (see **READLINE** below).
           **INSIDE_EMACS**
                  If this variable appears in the environment when the shell
                  starts, **bash** assumes that it is running inside an Emacs
                  shell buffer and may disable line editing, depending on the
                  value of **TERM**.
           **LANG** Used to determine the locale category for any category not
                  specifically selected with a variable starting with **LC_**.
           **LC_ALL** This variable overrides the value of **LANG** and any other **LC_**
                  variable specifying a locale category.
           **LC_COLLATE**
                  This variable determines the collation order used when
                  sorting the results of pathname expansion, and determines
                  the behavior of range expressions, equivalence classes, and
                  collating sequences within pathname expansion and pattern
                  matching.
           **LC_CTYPE**
                  This variable determines the interpretation of characters
                  and the behavior of character classes within pathname
                  expansion and pattern matching.
           **LC_MESSAGES**
                  This variable determines the locale used to translate
                  double-quoted strings preceded by a **$**.
           **LC_NUMERIC**
                  This variable determines the locale category used for
                  number formatting.
           **LC_TIME**
                  This variable determines the locale category used for data
                  and time formatting.
           **LINES** Used by the **select** compound command to determine the column
                  length for printing selection lists.  Automatically set if
                  the **checkwinsize** option is enabled or in an interactive
                  shell upon receipt of a **SIGWINCH**.
           **MAIL** If the value is set to a file or directory name and the
                  **MAILPATH** variable is not set, **bash** informs the user of the
                  arrival of mail in the specified file or Maildir-format
                  directory.
           **MAILCHECK**
                  Specifies how often (in seconds) **bash** checks for mail.  The
                  default is 60 seconds.  When it is time to check for mail,
                  the shell does so before displaying the primary prompt.  If
                  this variable is unset, or set to a value that is not a
                  number greater than or equal to zero, the shell disables
                  mail checking.
           **MAILPATH**
                  A colon-separated list of filenames to be checked for mail.
                  The message to be printed when mail arrives in a particular
                  file may be specified by separating the filename from the
                  message with a “?”.  When used in the text of the message,
                  **$_** expands to the name of the current mailfile.  For
                  example:
                  **MAILPATH** ='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
                  **Bash** can be configured to supply a default value for this
                  variable (there is no value by default), but the location
                  of the user mail files that it uses is system dependent
                  (e.g., /var/mail/**$USER**).
           **OPTERR** If set to the value 1, **bash** displays error messages
                  generated by the **getopts** builtin command (see **SHELL BUILTIN**
                  **COMMANDS** below).  **OPTERR** is initialized to 1 each time the
                  shell is invoked or a shell script is executed.
           **PATH** The search path for commands.  It is a colon-separated list
                  of directories in which the shell looks for commands (see
                  **COMMAND EXECUTION** below).  A zero-length (null) directory
                  name in the value of **PATH** indicates the current directory.
                  A null directory name may appear as two adjacent colons, or
                  as an initial or trailing colon.  The default path is
                  system-dependent, and is set by the administrator who
                  installs **bash**.  A common value is
                       /usr/local/bin:/usr/local/sbin:
                       /usr/bin:/usr/sbin:/bin:/sbin
           **POSIXLY_CORRECT**
                  If this variable is in the environment when **bash** starts,
                  the shell enters posix mode before reading the startup
                  files, as if the **--posix** invocation option had been
                  supplied.  If it is set while the shell is running, **bash**
                  enables posix mode, as if the command “set -o posix” had
                  been executed.  When the shell enters posix mode, it sets
                  this variable if it was not already set.
           **PROMPT_COMMAND**
                  If this variable is set, and is an array, the value of each
                  set element is executed as a command prior to issuing each
                  primary prompt.  If this is set but not an array variable,
                  its value is used as a command to execute instead.
           **PROMPT_DIRTRIM**
                  If set to a number greater than zero, the value is used as
                  the number of trailing directory components to retain when
                  expanding the **\w** and **\W** prompt string escapes (see
                  **PROMPTING** below).  Characters removed are replaced with an
                  ellipsis.
           **PS0** The value of this parameter is expanded (see **PROMPTING**
                  below) and displayed by interactive shells after reading a
                  command and before the command is executed.
           **PS1** The value of this parameter is expanded (see **PROMPTING**
                  below) and used as the primary prompt string.  The default
                  value is “\s-\v\$ ”.
           **PS2** The value of this parameter is expanded as with **PS1** and
                  used as the secondary prompt string.  The default is “> ”.
           **PS3** The value of this parameter is used as the prompt for the
                  **select** command (see **SHELL GRAMMAR** above).
           **PS4** The value of this parameter is expanded as with **PS1** and the
                  value is printed before each command **bash** displays during
                  an execution trace.  The first character of the expanded
                  value of **PS4** is replicated multiple times, as necessary, to
                  indicate multiple levels of indirection.  The default is
                  “+ ”.
           **SHELL** This variable expands to the full pathname to the shell.
                  If it is not set when the shell starts, **bash** assigns to it
                  the full pathname of the current user's login shell.
           **TIMEFORMAT**
                  The value of this parameter is used as a format string
                  specifying how the timing information for pipelines
                  prefixed with the **time** reserved word should be displayed.
                  The **%** character introduces an escape sequence that is
                  expanded to a time value or other information.  The escape
                  sequences and their meanings are as follows; the brackets
                  denote optional portions.
                  **%%** A literal **%**.
                  **%[**_p_**][l]R**
                         The elapsed time in seconds.
                  **%[**_p_**][l]U**
                         The number of CPU seconds spent in user mode.
                  **%[**_p_**][l]S**
                         The number of CPU seconds spent in system mode.
                  **%P** The CPU percentage, computed as (%U + %S) / %R.
    
                  The optional _p_ is a digit specifying the _precision_ , the
                  number of fractional digits after a decimal point.  A value
                  of 0 causes no decimal point or fraction to be output.
                  **time** prints at most six digits after the decimal point;
                  values of _p_ greater than 6 are changed to 6.  If _p_ is not
                  specified, **time** prints three digits after the decimal
                  point.
    
                  The optional **l** specifies a longer format, including
                  minutes, of the form _MM_ m _SS_._FF_ s.  The value of _p_ determines
                  whether or not the fraction is included.
    
                  If this variable is not set, **bash** acts as if it had the
                  value **$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'**.  If the value
                  is null, **bash** does not display any timing information.  A
                  trailing newline is added when the format string is
                  displayed.
           **TMOUT** If set to a value greater than zero, the **read** builtin uses
                  the value as its default timeout.  The **select** command
                  terminates if input does not arrive after **TMOUT** seconds
                  when input is coming from a terminal.  In an interactive
                  shell, the value is interpreted as the number of seconds to
                  wait for a line of input after issuing the primary prompt.
                  **Bash** terminates after waiting for that number of seconds if
                  a complete line of input does not arrive.
           **TMPDIR** If set, **bash** uses its value as the name of a directory in
                  which **bash** creates temporary files for the shell's use.
           **auto_resume**
                  This variable controls how the shell interacts with the
                  user and job control.  If this variable is set, simple
                  commands consisting of only a single word, without
                  redirections, are treated as candidates for resumption of
                  an existing stopped job.  There is no ambiguity allowed; if
                  there is more than one job beginning with or containing the
                  word, this selects the most recently accessed job.  The
                  _name_ of a stopped job, in this context, is the command line
                  used to start it, as displayed by **jobs**.  If set to the
                  value _exact_ , the word must match the name of a stopped job
                  exactly; if set to _substring_ , the word needs to match a
                  substring of the name of a stopped job.  The _substring_
                  value provides functionality analogous to the **%?** job
                  identifier (see **JOB CONTROL** below).  If set to any other
                  value (e.g., _prefix_), the word must be a prefix of a
                  stopped job's name; this provides functionality analogous
                  to the **%**_string_ job identifier.
           **histchars**
                  The two or three characters which control history
                  expansion, quick substitution, and tokenization (see
                  **HISTORY EXPANSION** below).  The first character is the
                  _history expansion_ character, the character which begins a
                  history expansion, normally “**!** ”.  The second character is
                  the _quick substitution_ character, normally “**^** ”.  When it
                  appears as the first character on the line, history
                  substitution repeats the previous command, replacing one
                  string with another.  The optional third character is the
                  _history comment_ character,  normally “**#** ”, which indicates
                  that the remainder of the line is a comment when it appears
                  as the first character of a word.  The history comment
                  character disables history substitution for the remaining
                  words on the line.  It does not necessarily cause the shell
                  parser to treat the rest of the line as a comment.
    
       **Arrays**
           **Bash** provides one-dimensional indexed and associative array
           variables.  Any variable may be used as an indexed array; the
           **declare** builtin explicitly declares an array.  There is no maximum
           limit on the size of an array, nor any requirement that members be
           indexed or assigned contiguously.  Indexed arrays are referenced
           using arithmetic expressions that must expand to an integer (see
           **ARITHMETIC EVALUATION** below) and are zero-based; associative
           arrays are referenced using arbitrary strings.  Unless otherwise
           noted, indexed array indices must be non-negative integers.
    
           The shell performs parameter and variable expansion, arithmetic
           expansion, command substitution, and quote removal on indexed
           array subscripts.  Since this can potentially result in empty
           strings, subscript indexing treats those as expressions that
           evaluate to 0.
    
           The shell performs tilde expansion, parameter and variable
           expansion, arithmetic expansion, command substitution, and quote
           removal on associative array subscripts.  Empty strings cannot be
           used as associative array keys.
    
           **Bash** automatically creates an indexed array if any variable is
           assigned to using the syntax
                  _name_[_subscript_]=_value_ .
           The _subscript_ is treated as an arithmetic expression that must
           evaluate to a number greater than or equal to zero.  To explicitly
           declare an indexed array, use
                  **declare -a** _name_
           (see **SHELL BUILTIN COMMANDS** below).
                  **declare -a** _name_[_subscript_]
           is also accepted; the _subscript_ is ignored.
    
           Associative arrays are created using
                  **declare -A** _name_
           .
    
           Attributes may be specified for an array variable using the
           **declare** and **readonly** builtins.  Each attribute applies to all
           members of an array.
    
           Arrays are assigned using compound assignments of the form
           _name_ =**(** value _1_ ... value _n_**)** , where each _value_ may be of the form
           [_subscript_]=_string_.  Indexed array assignments do not require
           anything but _string_.  Each _value_ in the list is expanded using the
           shell expansions described below under **EXPANSION** , but _value_ s that
           are valid variable assignments including the brackets and
           subscript do not undergo brace expansion and word splitting, as
           with individual variable assignments.
    
           When assigning to indexed arrays, if the optional brackets and
           subscript are supplied, that index is assigned to; otherwise the
           index of the element assigned is the last index assigned to by the
           statement plus one.  Indexing starts at zero.
    
           When assigning to an associative array, the words in a compound
           assignment may be either assignment statements, for which the
           subscript is required, or a list of words that is interpreted as a
           sequence of alternating keys and values: _name_ =**(**_key1 value1 key2_
           _value2_ ...**)**.  These are treated identically to _name_ =**(**
           [_key1_]=_value1_ [_key2_]=_value2_ ...**)**.  The first word in the list
           determines how the remaining words are interpreted; all
           assignments in a list must be of the same type.  When using
           key/value pairs, the keys may not be missing or empty; a final
           missing value is treated like the empty string.
    
           This syntax is also accepted by the **declare** builtin.  Individual
           array elements may be assigned to using the _name_[_subscript_]=_value_
           syntax introduced above.
    
           When assigning to an indexed array, if _name_ is subscripted by a
           negative number, that number is interpreted as relative to one
           greater than the maximum index of _name_ , so negative indices count
           back from the end of the array, and an index of -1 references the
           last element.
    
           The “+=” operator appends to an array variable when assigning
           using the compound assignment syntax; see **PARAMETERS** above.
    
           An array element is referenced using ${_name_[_subscript_]}.  The
           braces are required to avoid conflicts with pathname expansion.
           If _subscript_ is **@** or ***** , the word expands to all members of _name_ ,
           unless noted in the description of a builtin or word expansion.
           These subscripts differ only when the word appears within double
           quotes.  If the word is double-quoted, ${_name_[*]} expands to a
           single word with the value of each array member separated by the
           first character of the **IFS** special variable, and ${_name_[@]}
           expands each element of _name_ to a separate word.  When there are
           no array members, ${_name_[@]} expands to nothing.  If the double-
           quoted expansion occurs within a word, the expansion of the first
           parameter is joined with the beginning part of the expansion of
           the original word, and the expansion of the last parameter is
           joined with the last part of the expansion of the original word.
           This is analogous to the expansion of the special parameters ***** and
           **@**(see **Special Parameters** above).
    
           ${#_name_[_subscript_]} expands to the length of ${_name_[_subscript_]}.
           If _subscript_ is ***** or **@** , the expansion is the number of elements in
           the array.
    
           If the _subscript_ used to reference an element of an indexed array
           evaluates to a number less than zero, it is interpreted as
           relative to one greater than the maximum index of the array, so
           negative indices count back from the end of the array, and an
           index of -1 references the last element.
    
           Referencing an array variable without a subscript is equivalent to
           referencing the array with a subscript of 0.  Any reference to a
           variable using a valid subscript is valid; **bash** creates an array
           if necessary.
    
           An array variable is considered set if a subscript has been
           assigned a value.  The null string is a valid value.
    
           It is possible to obtain the keys (indices) of an array as well as
           the values.  ${**!**_name_[_@_]} and ${**!**_name_[_*_]} expand to the indices
           assigned in array variable _name_.  The treatment when in double
           quotes is similar to the expansion of the special parameters _@_ and
           _*_ within double quotes.
    
           The **unset** builtin is used to destroy arrays.  **unset**
           _name_[_subscript_] unsets the array element at index _subscript_ , for
           both indexed and associative arrays.  Negative subscripts to
           indexed arrays are interpreted as described above.  Unsetting the
           last element of an array variable does not unset the variable.
           **unset** _name_ , where _name_ is an array, removes the entire array.
           **unset** _name_[_subscript_] behaves differently depending on whether
           _name_ is an indexed or associative array when _subscript_ is ***** or **@**.
           If _name_ is an associative array, this unsets the element with
           subscript ***** or **@**.  If _name_ is an indexed array, unset removes all
           of the elements but does not remove the array itself.
    
           When using a variable name with a subscript as an argument to a
           command, such as with **unset** , without using the word expansion
           syntax described above, (e.g., unset a[4]), the argument is
           subject to pathname expansion.  Quote the argument if pathname
           expansion is not desired (e.g., unset 'a[4]').
    
           The **declare** , **local** , and **readonly** builtins each accept a **-a** option
           to specify an indexed array and a **-A** option to specify an
           associative array.  If both options are supplied, **-A** takes
           precedence.  The **read** builtin accepts a **-a** option to assign a list
           of words read from the standard input to an array.  The **set** and
           **declare** builtins display array values in a way that allows them to
           be reused as assignments.  Other builtins accept array name
           arguments as well (e.g., **mapfile**); see the descriptions of
           individual builtins below for details.  The shell provides a
           number of builtin array variables.
    


## EXPANSION



           Expansion is performed on the command line after it has been split
           into words.  The shell performs these expansions: _brace expansion_ ,
           _tilde expansion_ , _parameter and variable expansion_ , _command_
           _substitution_ , _arithmetic expansion_ , _word splitting_ , _pathname_
           _expansion_ , and _quote removal_.
    
           The order of expansions is: brace expansion; tilde expansion,
           parameter and variable expansion, arithmetic expansion, and
           command substitution (done in a left-to-right fashion); word
           splitting; pathname expansion; and quote removal.
    
           On systems that can support it, there is an additional expansion
           available: _process substitution_.  This is performed at the same
           time as tilde, parameter, variable, and arithmetic expansion and
           command substitution.
    
           _Quote removal_ is always performed last.  It removes quote
           characters present in the original word, not ones resulting from
           one of the other expansions, unless they have been quoted
           themselves.
    
           Only brace expansion, word splitting, and pathname expansion can
           increase the number of words of the expansion; other expansions
           expand a single word to a single word.  The only exceptions to
           this are the expansions of **"$@"** and **"${**_name_**[@]}"** , and, in most
           cases, **$*** and **${**_name_**[*]}** as explained above (see **PARAMETERS**).
    
       **Brace Expansion**
           _Brace expansion_ is a mechanism to generate arbitrary strings
           sharing a common prefix and suffix, either of which can be empty.
           This mechanism is similar to _pathname expansion_ , but the filenames
           generated need not exist.  Patterns to be brace expanded are
           formed from an optional _preamble_ , followed by either a series of
           comma-separated strings or a sequence expression between a pair of
           braces, followed by an optional _postscript_.  The preamble is
           prefixed to each string contained within the braces, and the
           postscript is then appended to each resulting string, expanding
           left to right.
    
           Brace expansions may be nested.  The results of each expanded
           string are not sorted; brace expansion preserves left to right
           order.  For example, a**{** d,c,b**}** e expands into “ade ace abe”.
    
           A sequence expression takes the form _x_**..**_y_**[..**_incr_**]** , where _x_ and _y_
           are either integers or single letters, and _incr_ , an optional
           increment, is an integer.  When integers are supplied, the
           expression expands to each number between _x_ and _y_ , inclusive.  If
           either _x_ or _y_ begins with a zero, each generated term will contain
           the same number of digits, zero-padding where necessary.  When
           letters are supplied, the expression expands to each character
           lexicographically between _x_ and _y_ , inclusive, using the C locale.
           Note that both _x_ and _y_ must be of the same type (integer or
           letter).  When the increment is supplied, it is used as the
           difference between each term.  The default increment is 1 or -1 as
           appropriate.
    
           Brace expansion is performed before any other expansions, and any
           characters special to other expansions are preserved in the
           result.  It is strictly textual.  **Bash** does not apply any
           syntactic interpretation to the context of the expansion or the
           text between the braces.
    
           A correctly-formed brace expansion must contain unquoted opening
           and closing braces, and at least one unquoted comma or a valid
           sequence expression.  Any incorrectly formed brace expansion is
           left unchanged.
    
           A “{” or Q , may be quoted with a backslash to prevent its being
           considered part of a brace expression.  To avoid conflicts with
           parameter expansion, the string “${” is not considered eligible
           for brace expansion, and inhibits brace expansion until the
           closing “}”.
    
           This construct is typically used as shorthand when the common
           prefix of the strings to be generated is longer than in the above
           example:
    
                  mkdir /usr/local/src/bash/{old,new,dist,bugs}
           or
                  chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
    
           Brace expansion introduces a slight incompatibility with
           historical versions of **sh**.  **sh** does not treat opening or closing
           braces specially when they appear as part of a word, and preserves
           them in the output.  **Bash** removes braces from words as a
           consequence of brace expansion.  For example, a word entered to **sh**
           as “file{1,2}” appears identically in the output.  **Bash** outputs
           that word as “file1 file2” after brace expansion.  Start **bash** with
           the **+B** option or disable brace expansion with the **+B** option to the
           **set** command (see **SHELL BUILTIN COMMANDS** below) for strict **sh**
           compatibility.
    
       **Tilde Expansion**
           If a word begins with an unquoted tilde character (“**~** ”), all of
           the characters preceding the first unquoted slash (or all
           characters, if there is no unquoted slash) are considered a _tilde-_
           _prefix_.  If none of the characters in the tilde-prefix are quoted,
           the characters in the tilde-prefix following the tilde are treated
           as a possible _login name_.  If this login name is the null string,
           the tilde is replaced with the value of the shell parameter **HOME**.
           If **HOME** is unset, the tilde expands to the home directory of the
           user executing the shell instead.  Otherwise, the tilde-prefix is
           replaced with the home directory associated with the specified
           login name.
    
           If the tilde-prefix is a “~+”, the value of the shell variable **PWD**
           replaces the tilde-prefix.  If the tilde-prefix is a “~-”, the
           shell substitutes the value of the shell variable **OLDPWD** , if it is
           set.  If the characters following the tilde in the tilde-prefix
           consist of a number _N_ , optionally prefixed by a “+” or a “-”, the
           tilde-prefix is replaced with the corresponding element from the
           directory stack, as it would be displayed by the **dirs** builtin
           invoked with the characters following the tilde in the tilde-
           prefix as an argument.  If the characters following the tilde in
           the tilde-prefix consist of a number without a leading “+” or “-”,
           tilde expansion assumes “+”.
    
           The results of tilde expansion are treated as if they were quoted,
           so the replacement is not subject to word splitting and pathname
           expansion.
    
           If the login name is invalid, or the tilde expansion fails, the
           tilde-prefix is unchanged.
    
           **Bash** checks each variable assignment for unquoted tilde-prefixes
           immediately following a **:** or the first **=** , and performs tilde
           expansion in these cases.  Consequently, one may use filenames
           with tildes in assignments to **PATH** , **MAILPATH** , and **CDPATH** , and the
           shell assigns the expanded value.
    
           **Bash** also performs tilde expansion on words satisfying the
           conditions of variable assignments (as described above under
           **PARAMETERS**) when they appear as arguments to simple commands.
           **Bash** does not do this, except for the _declaration_ commands listed
           above, when in posix mode.
    
       **Parameter Expansion**
           The “**$** ” character introduces parameter expansion, command
           substitution, or arithmetic expansion.  The parameter name or
           symbol to be expanded may be enclosed in braces, which are
           optional but serve to protect the variable to be expanded from
           characters immediately following it which could be interpreted as
           part of the name.
    
           When braces are used, the matching ending brace is the first “**}** ”
           not escaped by a backslash or within a quoted string, and not
           within an embedded arithmetic expansion, command substitution, or
           parameter expansion.
    
           The basic form of parameter expansion is
    
           ${_parameter_}
    
           which substitutes the value of _parameter_.  The braces are required
           when _parameter_ is a positional parameter with more than one digit,
           or when _parameter_ is followed by a character which is not to be
           interpreted as part of its name.  The _parameter_ is a shell
           parameter as described above **PARAMETERS**) or an array reference
           (**Arrays**).
    
           If the first character of _parameter_ is an exclamation point (**!**),
           and _parameter_ is not a _nameref_ , it introduces a level of
           indirection.  **Bash** uses the value formed by expanding the rest of
           _parameter_ as the new _parameter_ ; this new parameter is then
           expanded and that value is used in the rest of the expansion,
           rather than the expansion of the original _parameter_.  This is
           known as _indirect expansion_.  The value is subject to tilde
           expansion, parameter expansion, command substitution, and
           arithmetic expansion.  If _parameter_ is a nameref, this expands to
           the name of the parameter referenced by _parameter_ instead of
           performing the complete indirect expansion, for compatibility.
           The exceptions to this are the expansions of ${**!**_prefix_*****} and
           ${**!**_name_[_@_]} described below.  The exclamation point must
           immediately follow the left brace in order to introduce
           indirection.
    
           In each of the cases below, _word_ is subject to tilde expansion,
           parameter expansion, command substitution, and arithmetic
           expansion.
    
           When not performing substring expansion, using the forms
           documented below (e.g., **:-**), **bash** tests for a parameter that is
           unset or null.  Omitting the colon tests only for a parameter that
           is unset.
    
           ${_parameter_**:-**_word_}
                  **Use Default Values**.  If _parameter_ is unset or null, the
                  expansion of _word_ is substituted.  Otherwise, the value of
                  _parameter_ is substituted.
    
           ${_parameter_**:=**_word_}
                  **Assign Default Values**.  If _parameter_ is unset or null, the
                  expansion of _word_ is assigned to _parameter_ , and the
                  expansion is the final value of _parameter_.  Positional
                  parameters and special parameters may not be assigned in
                  this way.
    
           ${_parameter_**:?**_word_}
                  **Display Error if Null or Unset**.  If _parameter_ is null or
                  unset, the shell writes the expansion of _word_ (or a message
                  to that effect if _word_ is not present) to the standard
                  error and, if it is not interactive, exits with a non-zero
                  status.  An interactive shell does not exit, but does not
                  execute the command associated with the expansion.
                  Otherwise, the value of _parameter_ is substituted.
    
           ${_parameter_**:+**_word_}
                  **Use Alternate Value**.  If _parameter_ is null or unset,
                  nothing is substituted, otherwise the expansion of _word_ is
                  substituted.  The value of _parameter_ is not used.
    
           ${_parameter_**:**_offset_}
           ${_parameter_**:**_offset_**:**_length_}
                  **Substring Expansion**.  Expands to up to _length_ characters of
                  the value of _parameter_ starting at the character specified
                  by _offset_.  If _parameter_ is **@** or ***** , an indexed array
                  subscripted by **@** or ***** , or an associative array name, the
                  results differ as described below.  If **:**_length_ is omitted
                  (the first form above), this expands to the substring of
                  the value of _parameter_ starting at the character specified
                  by _offset_ and extending to the end of the value.  If _offset_
                  is omitted, it is treated as 0.  If _length_ is omitted, but
                  the colon after _offset_ is present, it is treated as 0.
                  _length_ and _offset_ are arithmetic expressions (see
                  **ARITHMETIC EVALUATION** below).
    
                  If _offset_ evaluates to a number less than zero, the value
                  is used as an offset in characters from the end of the
                  value of _parameter_.  If _length_ evaluates to a number less
                  than zero, it is interpreted as an offset in characters
                  from the end of the value of _parameter_ rather than a number
                  of characters, and the expansion is the characters between
                  _offset_ and that result.  Note that a negative offset must
                  be separated from the colon by at least one space to avoid
                  being confused with the **:-** expansion.
    
                  If _parameter_ is **@** or ***** , the result is _length_ positional
                  parameters beginning at _offset_.  A negative _offset_ is taken
                  relative to one greater than the greatest positional
                  parameter, so an offset of -1 evaluates to the last
                  positional parameter (or 0 if there are no positional
                  parameters).  It is an expansion error if _length_ evaluates
                  to a number less than zero.
    
                  If _parameter_ is an indexed array name subscripted by @ or
                  *, the result is the _length_ members of the array beginning
                  with ${_parameter_[_offset_]}.  A negative _offset_ is taken
                  relative to one greater than the maximum index of the
                  specified array.  It is an expansion error if _length_
                  evaluates to a number less than zero.
    
                  Substring expansion applied to an associative array
                  produces undefined results.
    
                  Substring indexing is zero-based unless the positional
                  parameters are used, in which case the indexing starts at 1
                  by default.  If _offset_ is 0, and the positional parameters
                  are used, **$0** is prefixed to the list.
    
           ${**!**_prefix_*****}
           ${**!**_prefix_**@**}
                  **Names matching prefix**.  Expands to the names of variables
                  whose names begin with _prefix_ , separated by the first
                  character of the **IFS** special variable.  When _@_ is used and
                  the expansion appears within double quotes, each variable
                  name expands to a separate word.
    
           ${**!**_name_[_@_]}
           ${**!**_name_[_*_]}
                  **List of array keys**.  If _name_ is an array variable, expands
                  to the list of array indices (keys) assigned in _name_.  If
                  _name_ is not an array, expands to 0 if _name_ is set and null
                  otherwise.  When _@_ is used and the expansion appears within
                  double quotes, each key expands to a separate word.
    
           ${**#**_parameter_}
                  **Parameter length**.  Substitutes the length in characters of
                  the expanded value of _parameter_.  If _parameter_ is ***** or **@** ,
                  the value substituted is the number of positional
                  parameters.  If _parameter_ is an array name subscripted by *****
                  or **@** , the value substituted is the number of elements in
                  the array.  If _parameter_ is an indexed array name
                  subscripted by a negative number, that number is
                  interpreted as relative to one greater than the maximum
                  index of _parameter_ , so negative indices count back from the
                  end of the array, and an index of -1 references the last
                  element.
    
           ${_parameter_**#**_word_}
           ${_parameter_**##**_word_}
                  **Remove matching prefix pattern**.  The _word_ is expanded to
                  produce a pattern just as in pathname expansion, and
                  matched against the expanded value of _parameter_ using the
                  rules described under **Pattern Matching** below.  If the
                  pattern matches the beginning of the value of _parameter_ ,
                  then the result of the expansion is the expanded value of
                  _parameter_ with the shortest matching pattern (the “#” case)
                  or the longest matching pattern (the “##” case) deleted.
                  If _parameter_ is **@** or ***** , the pattern removal operation is
                  applied to each positional parameter in turn, and the
                  expansion is the resultant list.  If _parameter_ is an array
                  variable subscripted with **@** or ***** , the pattern removal
                  operation is applied to each member of the array in turn,
                  and the expansion is the resultant list.
    
           ${_parameter_**%**_word_}
           ${_parameter_**%%**_word_}
                  **Remove matching suffix pattern**.  The _word_ is expanded to
                  produce a pattern just as in pathname expansion, and
                  matched against the expanded value of _parameter_ using the
                  rules described under **Pattern Matching** below.  If the
                  pattern matches a trailing portion of the expanded value of
                  _parameter_ , then the result of the expansion is the expanded
                  value of _parameter_ with the shortest matching pattern (the
                  “%” case) or the longest matching pattern (the “%%” case)
                  deleted.  If _parameter_ is **@** or ***** , the pattern removal
                  operation is applied to each positional parameter in turn,
                  and the expansion is the resultant list.  If _parameter_ is
                  an array variable subscripted with **@** or ***** , the pattern
                  removal operation is applied to each member of the array in
                  turn, and the expansion is the resultant list.
    
           ${_parameter_**/**_pattern_**/**_string_}
           ${_parameter_**//**_pattern_**/**_string_}
           ${_parameter_**/#**_pattern_**/**_string_}
           ${_parameter_**/%**_pattern_**/**_string_}
                  **Pattern substitution**.  The _pattern_ is expanded to produce a
                  pattern and matched against the expanded value of _parameter_
                  as described under **Pattern Matching** below.  The longest
                  match of _pattern_ in the expanded value is replaced with
                  _string_.  _string_ undergoes tilde expansion, parameter and
                  variable expansion, arithmetic expansion, command and
                  process substitution, and quote removal.
    
                  In the first form above, only the first match is replaced.
                  If there are two slashes separating _parameter_ and _pattern_
                  (the second form above), all matches of _pattern_ are
                  replaced with _string_.  If _pattern_ is preceded by **#**(the
                  third form above), it must match at the beginning of the
                  expanded value of _parameter_.  If _pattern_ is preceded by **%**
                  (the fourth form above), it must match at the end of the
                  expanded value of _parameter_.
    
                  If the expansion of _string_ is null, matches of _pattern_ are
                  deleted and the **/** following _pattern_ may be omitted.
    
                  If the **patsub_replacement** shell option is enabled using
                  **shopt** , any unquoted instances of **& **in _string_ are replaced
                  with the matching portion of _pattern_.
    
                  Quoting any part of _string_ inhibits replacement in the
                  expansion of the quoted portion, including replacement
                  strings stored in shell variables.  Backslash escapes **& **in
                  _string_ ; the backslash is removed in order to permit a
                  literal **& **in the replacement string.  Backslash can also be
                  used to escape a backslash; **\\** results in a literal
                  backslash in the replacement.  Users should take care if
                  _string_ is double-quoted to avoid unwanted interactions
                  between the backslash and double-quoting, since backslash
                  has special meaning within double quotes.  Pattern
                  substitution performs the check for unquoted **& **after
                  expanding _string_ ; shell programmers should quote any
                  occurrences of **& **they want to be taken literally in the
                  replacement and ensure any instances of **& **they want to be
                  replaced are unquoted.
    
                  Like the pattern removal operators, double quotes
                  surrounding the replacement string quote the expanded
                  characters, while double quotes enclosing the entire
                  parameter substitution do not, since the expansion is
                  performed in a context that doesn't take any enclosing
                  double quotes into account.
    
                  If the **nocasematch** shell option is enabled, the match is
                  performed without regard to the case of alphabetic
                  characters.
    
                  If _parameter_ is **@** or ***** , the substitution operation is
                  applied to each positional parameter in turn, and the
                  expansion is the resultant list.  If _parameter_ is an array
                  variable subscripted with **@** or ***** , the substitution
                  operation is applied to each member of the array in turn,
                  and the expansion is the resultant list.
    
           ${_parameter_**^**_pattern_}
           ${_parameter_**^^**_pattern_}
           ${_parameter_**,**_pattern_}
           ${_parameter_**,,**_pattern_}
                  **Case modification**.  This expansion modifies the case of
                  alphabetic characters in _parameter_.  First, the _pattern_ is
                  expanded to produce a pattern as described below under
                  **Pattern Matching**.  **Bash** then examines characters in the
                  expanded value of _parameter_ against _pattern_ as described
                  below.  If a character matches the pattern, its case is
                  converted.  The pattern should not attempt to match more
                  than one character.
    
                  Using “^” converts lowercase letters matching _pattern_ to
                  uppercase; “,” converts matching uppercase letters to
                  lowercase.  The **^** and **,** variants examine the first
                  character in the expanded value and convert its case if it
                  matches _pattern_ ; the **^^** and **,,** variants examine all
                  characters in the expanded value and convert each one that
                  matches _pattern_.  If _pattern_ is omitted, it is treated like
                  a **?** , which matches every character.
    
                  If _parameter_ is **@** or ***** , the case modification operation is
                  applied to each positional parameter in turn, and the
                  expansion is the resultant list.  If _parameter_ is an array
                  variable subscripted with **@** or ***** , the case modification
                  operation is applied to each member of the array in turn,
                  and the expansion is the resultant list.
    
           ${_parameter_**@**_operator_}
                  **Parameter transformation**.  The expansion is either a
                  transformation of the value of _parameter_ or information
                  about _parameter_ itself, depending on the value of _operator_.
                  Each _operator_ is a single letter:
                  **U** The expansion is a string that is the value of
                         _parameter_ with lowercase alphabetic characters
                         converted to uppercase.
                  **u** The expansion is a string that is the value of
                         _parameter_ with the first character converted to
                         uppercase, if it is alphabetic.
                  **L** The expansion is a string that is the value of
                         _parameter_ with uppercase alphabetic characters
                         converted to lowercase.
                  **Q** The expansion is a string that is the value of
                         _parameter_ quoted in a format that can be reused as
                         input.
                  **E** The expansion is a string that is the value of
                         _parameter_ with backslash escape sequences expanded
                         as with the **$'**...**'** quoting mechanism.
                  **P** The expansion is a string that is the result of
                         expanding the value of _parameter_ as if it were a
                         prompt string (see **PROMPTING** below).
                  **A** The expansion is a string in the form of an
                         assignment statement or **declare** command that, if
                         evaluated, recreates _parameter_ with its attributes
                         and value.
                  **K** Produces a possibly-quoted version of the value of
                         _parameter_ , except that it prints the values of
                         indexed and associative arrays as a sequence of
                         quoted key-value pairs (see **Arrays** above).  The keys
                         and values are quoted in a format that can be reused
                         as input.
                  **a** The expansion is a string consisting of flag values
                         representing _parameter_ 's attributes.
                  **k** Like the K transformation, but expands the keys and
                         values of indexed and associative arrays to separate
                         words after word splitting.
    
                  If _parameter_ is **@** or ***** , the operation is applied to each
                  positional parameter in turn, and the expansion is the
                  resultant list.  If _parameter_ is an array variable
                  subscripted with **@** or ***** , the operation is applied to each
                  member of the array in turn, and the expansion is the
                  resultant list.
    
                  The result of the expansion is subject to word splitting
                  and pathname expansion as described below.
    
       **Command Substitution**
           _Command substitution_ allows the output of a command to replace the
           command itself.  There are two standard forms:
    
                  **$(**_command_**)**
           or (deprecated)
                  **`**_command_**`**.
    
           **Bash** performs the expansion by executing _command_ in a subshell
           environment and replacing the command substitution with the
           standard output of the command, with any trailing newlines
           deleted.  Embedded newlines are not deleted, but they may be
           removed during word splitting.  The command substitution **$(cat**
           _file_**)** can be replaced by the equivalent but faster **$( < **_file_**)**.
    
           With the old-style backquote form of substitution, backslash
           retains its literal meaning except when followed by **$** , **`** , or **\**.
           The first backquote not preceded by a backslash terminates the
           command substitution.  When using the $(_command_) form, all
           characters between the parentheses make up the command; none are
           treated specially.
    
           There is an alternate form of command substitution:
    
                  **${**_c command_**;}**
    
           which executes _command_ in the current execution environment and
           captures its output, again with trailing newlines removed.
    
           The character _c_ following the open brace must be a space, tab,
           newline, or **|** , and the close brace must be in a position where a
           reserved word may appear (i.e., preceded by a command terminator
           such as semicolon).  **Bash** allows the close brace to be joined to
           the remaining characters in the word without being followed by a
           shell metacharacter as a reserved word would usually require.
    
           Any side effects of _command_ take effect immediately in the current
           execution environment and persist in the current environment after
           the command completes (e.g., the **exit** builtin exits the shell).
    
           This type of command substitution superficially resembles
           executing an unnamed shell function: local variables are created
           as when a shell function is executing, and the **return** builtin
           forces _command_ to complete; however, the rest of the execution
           environment, including the positional parameters, is shared with
           the caller.
    
           If the first character following the open brace is a **|** , the
           construct expands to the value of the **REPLY** shell variable after
           _command_ executes, without removing any trailing newlines, and the
           standard output of _command_ remains the same as in the calling
           shell.  **Bash** creates **REPLY** as an initially-unset local variable
           when _command_ executes, and restores **REPLY** to the value it had
           before the command substitution after _command_ completes, as with
           any local variable.
    
           Command substitutions may be nested.  To nest when using the
           backquoted form, escape the inner backquotes with backslashes.
    
           If the substitution appears within double quotes, **bash** does not
           perform word splitting and pathname expansion on the results.
    
       **Arithmetic Expansion**
           Arithmetic expansion evaluates an arithmetic expression and
           substitutes the result.  The format for arithmetic expansion is:
    
                  **$((**_expression_**))**
    
           The _expression_ undergoes the same expansions as if it were within
           double quotes, but unescaped double quote characters in _expression_
           are not treated specially and are removed.  All tokens in the
           expression undergo parameter and variable expansion, command
           substitution, and quote removal.  The result is treated as the
           arithmetic expression to be evaluated.  Since the way Bash handles
           double quotes can potentially result in empty strings, arithmetic
           expansion treats those as expressions that evaluate to 0.
           Arithmetic expansions may be nested.
    
           The evaluation is performed according to the rules listed below
           under **ARITHMETIC EVALUATION**.  If _expression_ is invalid, **bash**
           prints a message to standard error indicating failure, does not
           perform the substitution, and does not execute the command
           associated with the expansion.
    
       **Process Substitution**
           _Process substitution_ allows a process's input or output to be
           referred to using a filename.  It takes the form of **<(**_list_**)** or
           **>(**_list_**)**.  The process _list_ is run asynchronously, and its input or
           output appears as a filename.  This filename is passed as an
           argument to the current command as the result of the expansion.
    
           If the **>(**_list_**)** form is used, writing to the file provides input
           for _list_.  If the **<(**_list_**)** form is used, reading the file obtains
           the output of _list_.  No space may appear between the **< **or **> **and
           the left parenthesis, otherwise the construct would be interpreted
           as a redirection.
    
           Process substitution is supported on systems that support named
           pipes (_FIFOs_) or the _/dev/fd_ method of naming open files.
    
           When available, process substitution is performed simultaneously
           with parameter and variable expansion, command substitution, and
           arithmetic expansion.
    
       **Word Splitting**
           The shell scans the results of parameter expansion, command
           substitution, and arithmetic expansion that did not occur within
           double quotes for _word splitting_.  Words that were not expanded
           are not split.
    
           The shell treats each character of **IFS** as a delimiter, and splits
           the results of the other expansions into words using these
           characters as field terminators.
    
           An _IFS whitespace_ character is whitespace as defined above (see
           **Definitions**) that appears in the value of **IFS**.  Space, tab, and
           newline are always considered IFS whitespace, even if they don't
           appear in the locale's **space** category.
    
           If **IFS** is unset, field splitting acts as if its value were
           **< space><tab><newline>**, and treats these characters as IFS
           whitespace.  If the value of **IFS** is null, no word splitting
           occurs, but implicit null arguments (see below) are still removed.
    
           Word splitting begins by removing sequences of IFS whitespace
           characters from the beginning and end of the results of the
           previous expansions, then splits the remaining words.
    
           If the value of **IFS** consists solely of IFS whitespace, any
           sequence of IFS whitespace characters delimits a field, so a field
           consists of characters that are not unquoted IFS whitespace, and
           null fields result only from quoting.
    
           If **IFS** contains a non-whitespace character, then any character in
           the value of **IFS** that is not IFS whitespace, along with any
           adjacent IFS whitespace characters, delimits a field.  This means
           that adjacent non-IFS-whitespace delimiters produce a null field.
           A sequence of IFS whitespace characters also delimits a field.
    
           Explicit null arguments (**""** or **''**) are retained and passed to
           commands as empty strings.  Unquoted implicit null arguments,
           resulting from the expansion of parameters that have no values,
           are removed.  Expanding a parameter with no value within double
           quotes produces a null field, which is retained and passed to a
           command as an empty string.
    
           When a quoted null argument appears as part of a word whose
           expansion is non-null, word splitting removes the null argument
           portion, leaving the non-null expansion.  That is, the word “-d''”
           becomes “-d” after word splitting and null argument removal.
    
       **Pathname Expansion**
           After word splitting, unless the **-f** option has been set, **bash**
           scans each word for the characters ***** , **?** , and **[**.  If one of these
           characters appears, and is not quoted, then the word is regarded
           as a _pattern_ , and replaced with a sorted list of filenames
           matching the pattern (see **Pattern Matching** below) subject to the
           value of the **GLOBSORT** shell variable.
    
           If no matching filenames are found, and the shell option **nullglob**
           is not enabled, the word is left unchanged.  If the **nullglob**
           option is set, and no matches are found, the word is removed.  If
           the **failglob** shell option is set, and no matches are found, **bash**
           prints an error message and does not execute the command.  If the
           shell option **nocaseglob** is enabled, the match is performed without
           regard to the case of alphabetic characters.
    
           When a pattern is used for pathname expansion, the character “.”
           at the start of a name or immediately following a slash must be
           matched explicitly, unless the shell option **dotglob** is set.  In
           order to match the filenames _._ and _.._ , the pattern must begin with
           “.” (for example, “.?”), even if **dotglob** is set.  If the
           **globskipdots** shell option is enabled, the filenames _._ and _.._ never
           match, even if the pattern begins with a “.”.  When not matching
           pathnames, the “.” character is not treated specially.
    
           When matching a pathname, the slash character must always be
           matched explicitly by a slash in the pattern, but in other
           matching contexts it can be matched by a special pattern character
           as described below under **Pattern Matching**.
    
           See the description of **shopt** below under **SHELL BUILTIN COMMANDS**
           for a description of the **nocaseglob** , **nullglob** , **globskipdots** ,
           **failglob** , and **dotglob** shell options.
    
           The **GLOBIGNORE** shell variable may be used to restrict the set of
           file names matching a _pattern_.  If **GLOBIGNORE** is set, each
           matching file name that also matches one of the patterns in
           **GLOBIGNORE** is removed from the list of matches.  If the **nocaseglob**
           option is set, the matching against the patterns in **GLOBIGNORE** is
           performed without regard to case.  The filenames _._ and _.._ are
           always ignored when **GLOBIGNORE** is set and not null.  However,
           setting **GLOBIGNORE** to a non-null value has the effect of enabling
           the **dotglob** shell option, so all other filenames beginning with a
           “.” match.  To get the old behavior of ignoring filenames
           beginning with a “.”, make “.*”  one of the patterns in
           **GLOBIGNORE**.  The **dotglob** option is disabled when **GLOBIGNORE** is
           unset.  The **GLOBIGNORE** pattern matching honors the setting of the
           **extglob** shell option.
    
           The value of the **GLOBSORT** shell variable controls how the results
           of pathname expansion are sorted, as described above under **Shell**
           **Variables**.
    
           **Pattern Matching**
    
           Any character that appears in a pattern, other than the special
           pattern characters described below, matches itself.  The NUL
           character may not occur in a pattern.  A backslash escapes the
           following character; the escaping backslash is discarded when
           matching.  The special pattern characters must be quoted if they
           are to be matched literally.
    
           The special pattern characters have the following meanings:
    
                  ***** Matches any string, including the null string.  When
                         the **globstar** shell option is enabled, and ***** is used
                         in a pathname expansion context, two adjacent ***** s
                         used as a single pattern match all files and zero or
                         more directories and subdirectories.  If followed by
                         a **/** , two adjacent ***** s match only directories and
                         subdirectories.
                  **?** Matches any single character.
                  **[**...**]** Matches any one of the characters enclosed between
                         the brackets.  This is known as a _bracket expression_
                         and matches a single character.  A pair of
                         characters separated by a hyphen denotes a _range_
                         _expression_ ; any character that falls between those
                         two characters, inclusive, using the current
                         locale's collating sequence and character set,
                         matches.  If the first character following the **[** is
                         a **!** or a **^** then any character not within the range
                         matches.  To match a **-** , include it as the first or
                         last character in the set.  To match a **]** , include it
                         as the first character in the set.
    
                         The sorting order of characters in range
                         expressions, and the characters included in the
                         range, are determined by the current locale and the
                         values of the **LC_COLLATE** or **LC_ALL** shell variables,
                         if set.  To obtain the traditional interpretation of
                         range expressions, where **[a-d]** is equivalent to
                         **[abcd]** , set the value of the **LC_COLLATE** or **LC_ALL**
                         shell variables to **C** , or enable the **globasciiranges**
                         shell option.
    
                         Within a bracket expression, _character classes_ can
                         be specified using the syntax **[:**_class_**:]** , where _class_
                         is one of the following classes defined in the POSIX
                         standard:
    
                         **alnum alpha ascii blank cntrl digit graph lower**
                         **print punct space upper word xdigit**
    
                         A character class matches any character belonging to
                         that class.  The **word** character class matches
                         letters, digits, and the character _.
    
                         Within a bracket expression, an _equivalence class_
                         can be specified using the syntax **[=**_c_**=]** , which
                         matches all characters with the same collation
                         weight (as defined by the current locale) as the
                         character _c_.
    
                         Within a bracket expression, the syntax **[.**_symbol_**.]**
                         matches the collating symbol _symbol_.
    
           If the **extglob** shell option is enabled using the **shopt** builtin,
           the shell recognizes several extended pattern matching operators.
           In the following description, a _pattern-list_ is a list of one or
           more patterns separated by a **|**.  Composite patterns may be formed
           using one or more of the following sub-patterns:
    
                  **?(**_pattern-list_**)**
                         Matches zero or one occurrence of the given
                         patterns.
                  ***(**_pattern-list_**)**
                         Matches zero or more occurrences of the given
                         patterns.
                  **+(**_pattern-list_**)**
                         Matches one or more occurrences of the given
                         patterns.
                  **@(**_pattern-list_**)**
                         Matches one of the given patterns.
                  **!(**_pattern-list_**)**
                         Matches anything except one of the given patterns.
    
           The **extglob** option changes the behavior of the parser, since the
           parentheses are normally treated as operators with syntactic
           meaning.  To ensure that extended matching patterns are parsed
           correctly, make sure that **extglob** is enabled before parsing
           constructs containing the patterns, including shell functions and
           command substitutions.
    
           When matching filenames, the **dotglob** shell option determines the
           set of filenames that are tested: when **dotglob** is enabled, the set
           of filenames includes all files beginning with “.”, but _._ and _.._
           must be matched by a pattern or sub-pattern that begins with a
           dot; when it is disabled, the set does not include any filenames
           beginning with “.” unless the pattern or sub-pattern begins with a
           “.”.  If the **globskipdots** shell option is enabled, the filenames _._
           and _.._ never appear in the set.  As above, “.” only has a special
           meaning when matching filenames.
    
           Complicated extended pattern matching against long strings is
           slow, especially when the patterns contain alternations and the
           strings contain multiple matches.  Using separate matches against
           shorter strings, or using arrays of strings instead of a single
           long string, may be faster.
    
       **Quote Removal**
           After the preceding expansions, all unquoted occurrences of the
           characters **\** , **'** , and **"** that did not result from one of the above
           expansions are removed.
    


## REDIRECTION



           Before a command is executed, its input and output may be
           _redirected_ using a special notation interpreted by the shell.
           _Redirection_ allows commands' file handles to be duplicated,
           opened, closed, made to refer to different files, and can change
           the files the command reads from and writes to.  When used with
           the **exec** builtin, redirections modify file handles in the current
           shell execution environment.  The following redirection operators
           may precede or appear anywhere within a _simple command_ or may
           follow a _command_.  Redirections are processed in the order they
           appear, from left to right.
    
           Each redirection that may be preceded by a file descriptor number
           may instead be preceded by a word of the form {_varname_}.  In this
           case, for each redirection operator except **> &- **and **< &-**, the shell
           allocates a file descriptor greater than or equal to 10 and
           assigns it to _varname_.  If {_varname_} precedes **> &- **or **< &-**, the
           value of _varname_ defines the file descriptor to close.  If
           {_varname_} is supplied, the redirection persists beyond the scope
           of the command, which allows the shell programmer to manage the
           file descriptor's lifetime manually without using the **exec**
           builtin.  The **varredir_close** shell option manages this behavior.
    
           In the following descriptions, if the file descriptor number is
           omitted, and the first character of the redirection operator is
           “<”, the redirection refers to the standard input (file descriptor
           0).  If the first character of the redirection operator is “>”,
           the redirection refers to the standard output (file descriptor 1).
    
           The _word_ following the redirection operator in the following
           descriptions, unless otherwise noted, is subjected to brace
           expansion, tilde expansion, parameter and variable expansion,
           command substitution, arithmetic expansion, quote removal,
           pathname expansion, and word splitting.  If it expands to more
           than one word, **bash** reports an error.
    
           The order of redirections is significant.  For example, the
           command
    
                  ls **> **dirlist 2**> &**1
    
           directs both standard output and standard error to the file
           _dirlist_ , while the command
    
                  ls 2**> &**1 **> **dirlist
    
           directs only the standard output to file _dirlist_ , because the
           standard error was directed to the standard output before the
           standard output was redirected to _dirlist_.
    
           **Bash** handles several filenames specially when they are used in
           redirections, as described in the following table.  If the
           operating system on which **bash** is running provides these special
           files, **bash** uses them; otherwise it emulates them internally with
           the behavior described below.
    
                  **/dev/fd/**_fd_
                         If _fd_ is a valid integer, duplicate file descriptor
                         _fd_.
                  **/dev/stdin**
                         File descriptor 0 is duplicated.
                  **/dev/stdout**
                         File descriptor 1 is duplicated.
                  **/dev/stderr**
                         File descriptor 2 is duplicated.
                  **/dev/tcp/**_host_**/**_port_
                         If _host_ is a valid hostname or Internet address, and
                         _port_ is an integer port number or service name, **bash**
                         attempts to open the corresponding TCP socket.
                  **/dev/udp/**_host_**/**_port_
                         If _host_ is a valid hostname or Internet address, and
                         _port_ is an integer port number or service name, **bash**
                         attempts to open the corresponding UDP socket.
    
           A failure to open or create a file causes the redirection to fail.
    
           Redirections using file descriptors greater than 9 should be used
           with care, as they may conflict with file descriptors the shell
           uses internally.
    
       **Redirecting Input**
           Redirecting input opens the file whose name results from the
           expansion of _word_ for reading on file descriptor _n_ , or the
           standard input (file descriptor 0) if _n_ is not specified.
    
           The general format for redirecting input is:
    
                  [_n_]**<**_word_
    
       **Redirecting Output**
           Redirecting output opens the file whose name results from the
           expansion of _word_ for writing on file descriptor _n_ , or the
           standard output (file descriptor 1) if _n_ is not specified.  If the
           file does not exist it is created; if it does exist it is
           truncated to zero size.
    
           The general format for redirecting output is:
    
                  [_n_]**>**_word_
    
           If the redirection operator is **>** , and the **noclobber** option to the
           **set** builtin command has been enabled, the redirection fails if the
           file whose name results from the expansion of _word_ exists and is a
           regular file.  If the redirection operator is **> |**, or the
           redirection operator is **> **and the **noclobber** option to the **set**
           builtin is not enabled, **bash** attempts the redirection even if the
           file named by _word_ exists.
    
       **Appending Redirected Output**
           Redirecting output in this fashion opens the file whose name
           results from the expansion of _word_ for appending on file
           descriptor _n_ , or the standard output (file descriptor 1) if _n_ is
           not specified.  If the file does not exist it is created.
    
           The general format for appending output is:
    
                  [_n_]**> >**_word_
    
       **Redirecting Standard Output and Standard Error**
           This construct redirects both the standard output (file descriptor
           1) and the standard error output (file descriptor 2) to the file
           whose name is the expansion of _word_.
    
           There are two formats for redirecting standard output and standard
           error:
    
                  **& >**_word_
           and
                  **> &**_word_
    
           Of the two forms, the first is preferred.  This is semantically
           equivalent to
    
                  **>**_word_ 2**> &**1
    
           When using the second form, _word_ may not expand to a number or **-**.
           If it does, other redirection operators apply (see **Duplicating**
           **File Descriptors** below) for compatibility reasons.
    
       **Appending Standard Output and Standard Error**
           This construct appends both the standard output (file descriptor
           1) and the standard error output (file descriptor 2) to the file
           whose name is the expansion of _word_.
    
           The format for appending standard output and standard error is:
    
                  **& >>**_word_
    
           This is semantically equivalent to
    
                  **> >**_word_ 2**> &**1
    
           (see **Duplicating File Descriptors** below).
    
       **Here Documents**
           This type of redirection instructs the shell to read input from
           the current source until it reads a line containing only _delimiter_
           (with no trailing blanks).  All of the lines read up to that point
           then become the standard input (or file descriptor _n_ if _n_ is
           specified) for a command.
    
           The format of here-documents is:
    
                  [_n_]**< <**[**-**]_word_
                          _here-document_
                  _delimiter_
    
           The shell does not perform parameter and variable expansion,
           command substitution, arithmetic expansion, or pathname expansion
           on _word_.
    
           If any part of _word_ is quoted, the _delimiter_ is the result of
           quote removal on _word_ , and the lines in the here-document are not
           expanded.  If _word_ is unquoted, the _delimiter_ is _word_ itself, and
           the here-document text is treated similarly to a double-quoted
           string: all lines of the here-document are subjected to parameter
           expansion, command substitution, and arithmetic expansion, the
           character sequence **\ <newline> **is treated literally, and **\** must be
           used to quote the characters **\** , **$** , and **`** ; however, double quote
           characters have no special meaning.
    
           If the redirection operator is **< <-**, then the shell strips all
           leading tab characters from input lines and the line containing
           _delimiter_.  This allows here-documents within shell scripts to be
           indented in a natural fashion.
    
           If the delimiter is not quoted, the **\ <newline> **sequence is treated
           as a line continuation: the two lines are joined and the
           backslash-newline is removed.  This happens while reading the
           here-document, before the check for the ending delimiter, so
           joined lines can form the end delimiter.
    
       **Here Strings**
           A variant of here documents, the format is:
    
                  [_n_]**< <<**_word_
    
           The _word_ undergoes tilde expansion, parameter and variable
           expansion, command substitution, arithmetic expansion, and quote
           removal.  Pathname expansion and word splitting are not performed.
           The result is supplied as a single string, with a newline
           appended, to the command on its standard input (or file descriptor
           _n_ if _n_ is specified).
    
       **Duplicating File Descriptors**
           The redirection operator
    
                  [_n_]**< &**_word_
    
           is used to duplicate input file descriptors.  If _word_ expands to
           one or more digits, file descriptor _n_ is made to be a copy of that
           file descriptor.  It is a redirection error if the digits in _word_
           do not specify a file descriptor open for input.  If _word_
           evaluates to **-** , file descriptor _n_ is closed.  If _n_ is not
           specified, this uses the standard input (file descriptor 0).
    
           The operator
    
                  [_n_]**> &**_word_
    
           is used similarly to duplicate output file descriptors.  If _n_ is
           not specified, this uses the standard output (file descriptor 1).
           It is a redirection error if the digits in _word_ do not specify a
           file descriptor open for output.  If _word_ evaluates to **-** , file
           descriptor _n_ is closed.  As a special case, if _n_ is omitted, and
           _word_ does not expand to one or more digits or **-** , this redirects
           the standard output and standard error as described previously.
    
       **Moving File Descriptors**
           The redirection operator
    
                  [_n_]**< &**_digit_**-**
    
           moves the file descriptor _digit_ to file descriptor _n_ , or the
           standard input (file descriptor 0) if _n_ is not specified.  _digit_
           is closed after being duplicated to _n_.
    
           Similarly, the redirection operator
    
                  [_n_]**> &**_digit_**-**
    
           moves the file descriptor _digit_ to file descriptor _n_ , or the
           standard output (file descriptor 1) if _n_ is not specified.
    
       **Opening File Descriptors for Reading and Writing**
           The redirection operator
    
                  [_n_]**< >**_word_
    
           opens the file whose name is the expansion of _word_ for both
           reading and writing on file descriptor _n_ , or on file descriptor 0
           if _n_ is not specified.  If the file does not exist, it is created.
    


## ALIASES



           _Aliases_ allow a string to be substituted for a word that is in a
           position in the input where it can be the first word of a simple
           command.  Aliases have names and corresponding values that are set
           and unset using the **alias** and **unalias** builtin commands (see **SHELL**
           **BUILTIN COMMANDS** below).
    
           If the shell reads an unquoted word in the right position, it
           checks the word to see if it matches an alias name.  If it
           matches, the shell replaces the word with the alias value, and
           reads that value as if it had been read instead of the word.  The
           shell doesn't look at any characters following the word before
           attempting alias substitution.
    
           The characters **/** , **$** , **`** , and **=** and any of the shell _metacharacters_
           or quoting characters listed above may not appear in an alias
           name.  The replacement text may contain any valid shell input,
           including shell metacharacters.  The first word of the replacement
           text is tested for aliases, but a word that is identical to an
           alias being expanded is not expanded a second time.  This means
           that one may alias **ls** to **ls -F** , for instance, and **bash** does not
           try to recursively expand the replacement text.
    
           If the last character of the alias value is a _blank_ , the shell
           checks the next command word following the alias for alias
           expansion.
    
           Aliases are created and listed with the **alias** command, and removed
           with the **unalias** command.
    
           There is no mechanism for using arguments in the replacement text.
           If arguments are needed, use a shell function (see **FUNCTIONS**
           below) instead.
    
           Aliases are not expanded when the shell is not interactive, unless
           the **expand_aliases** shell option is set using **shopt**(see the
           description of **shopt** under **SHELL BUILTIN COMMANDS** below).
    
           The rules concerning the definition and use of aliases are
           somewhat confusing.  **Bash** always reads at least one complete line
           of input, and all lines that make up a compound command, before
           executing any of the commands on that line or the compound
           command.  Aliases are expanded when a command is read, not when it
           is executed.  Therefore, an alias definition appearing on the same
           line as another command does not take effect until the shell reads
           the next line of input, and an alias definition in a compound
           command does not take effect until the shell parses and executes
           the entire compound command.  The commands following the alias
           definition on that line, or in the rest of a compound command, are
           not affected by the new alias.  This behavior is also an issue
           when functions are executed.  Aliases are expanded when a function
           definition is read, not when the function is executed, because a
           function definition is itself a command.  As a consequence,
           aliases defined in a function are not available until after that
           function is executed.  To be safe, always put alias definitions on
           a separate line, and do not use **alias** in compound commands.
    
           For almost every purpose, shell functions are preferable to
           aliases.
    


## FUNCTIONS



           A shell function, defined as described above under **SHELL GRAMMAR** ,
           stores a series of commands for later execution.  When the name of
           a shell function is used as a simple command name, the shell
           executes the list of commands associated with that function name.
           Functions are executed in the context of the calling shell; there
           is no new process created to interpret them (contrast this with
           the execution of a shell script).
    
           When a function is executed, the arguments to the function become
           the positional parameters during its execution.  The special
           parameter **#** is updated to reflect the new positional parameters.
           Special parameter **0** is unchanged.  The first element of the
           **FUNCNAME** variable is set to the name of the function while the
           function is executing.
    
           All other aspects of the shell execution environment are identical
           between a function and its caller with these exceptions: the **DEBUG**
           and **RETURN** traps (see the description of the **trap** builtin under
           **SHELL BUILTIN COMMANDS** below) are not inherited unless the
           function has been given the **trace** attribute (see the description
           of the **declare** builtin below) or the **-o functrace** shell option has
           been enabled with the **set** builtin (in which case all functions
           inherit the **DEBUG** and **RETURN** traps), and the **ERR** trap is not
           inherited unless the **-o errtrace** shell option has been enabled.
    
           Variables local to the function are declared with the **local**
           builtin command (_local variables_).  Ordinarily, variables and
           their values are shared between the function and its caller.  If a
           variable is declared **local** , the variable's visible scope is
           restricted to that function and its children (including the
           functions it calls).
    
           In the following description, the _current scope_ is a currently-
           executing function.  Previous scopes consist of that function's
           caller and so on, back to the “global” scope, where the shell is
           not executing any shell function.  A local variable at the current
           scope is a variable declared using the **local** or **declare** builtins
           in the function that is currently executing.
    
           Local variables “shadow” variables with the same name declared at
           previous scopes.  For instance, a local variable declared in a
           function hides variables with the same name declared at previous
           scopes, including global variables: references and assignments
           refer to the local variable, leaving the variables at previous
           scopes unmodified.  When the function returns, the global variable
           is once again visible.
    
           The shell uses _dynamic scoping_ to control a variable's visibility
           within functions.  With dynamic scoping, visible variables and
           their values are a result of the sequence of function calls that
           caused execution to reach the current function.  The value of a
           variable that a function sees depends on its value within its
           caller, if any, whether that caller is the global scope or another
           shell function.  This is also the value that a local variable
           declaration shadows, and the value that is restored when the
           function returns.
    
           For example, if a variable _var_ is declared as local in function
           _func1_ , and _func1_ calls another function _func2_ , references to _var_
           made from within _func2_ resolve to the local variable _var_ from
           _func1_ , shadowing any global variable named _var_.
    
           The **unset** builtin also acts using the same dynamic scope: if a
           variable is local to the current scope, **unset** unsets it; otherwise
           the unset will refer to the variable found in any calling scope as
           described above.  If a variable at the current local scope is
           unset, it remains so (appearing as unset) until it is reset in
           that scope or until the function returns.  Once the function
           returns, any instance of the variable at a previous scope becomes
           visible.  If the unset acts on a variable at a previous scope, any
           instance of a variable with that name that had been shadowed
           becomes visible (see below how the **localvar_unset** shell option
           changes this behavior).
    
           The **FUNCNEST** variable, if set to a numeric value greater than 0,
           defines a maximum function nesting level.  Function invocations
           that exceed the limit cause the entire command to abort.
    
           If the builtin command **return** is executed in a function, the
           function completes and execution resumes with the next command
           after the function call.  If **return** is supplied a numeric
           argument, that is the function's return status; otherwise the
           function's return status is the exit status of the last command
           executed before the **return**.  Any command associated with the
           **RETURN** trap is executed before execution resumes.  When a function
           completes, the values of the positional parameters and the special
           parameter **#** are restored to the values they had prior to the
           function's execution.
    
           The **-f** option to the **declare** or **typeset** builtin commands lists
           function names and definitions.  The **-F** option to **declare** or
           **typeset** lists the function names only (and optionally the source
           file and line number, if the **extdebug** shell option is enabled).
           Functions may be exported so that child shell processes (those
           created when executing a separate shell invocation) automatically
           have them defined with the **-f** option to the **export** builtin.  The
           **-f** option to the **unset** builtin deletes a function definition.
    
           Functions may be recursive.  The **FUNCNEST** variable may be used to
           limit the depth of the function call stack and restrict the number
           of function invocations.  By default, **bash** imposes no limit on the
           number of recursive calls.
    


## ARITHMETIC EVALUATION



           The shell allows arithmetic expressions to be evaluated, under
           certain circumstances (see the **let** and **declare** builtin commands,
           the **((** compound command, the arithmetic **for** command, the **[[**
           conditional command, and **Arithmetic Expansion**).
    
           Evaluation is done in the largest fixed-width integers available,
           with no check for overflow, though division by 0 is trapped and
           flagged as an error.  The operators and their precedence,
           associativity, and values are the same as in the C language.  The
           following list of operators is grouped into levels of equal-
           precedence operators.  The levels are listed in order of
           decreasing precedence.
    
           _id_**++**_id_**--**
                  variable post-increment and post-decrement
           **++**_id_ **--**_id_
                  variable pre-increment and pre-decrement
           **- +** unary minus and plus
           **! ~** logical and bitwise negation
           ****** exponentiation
           *** / %** multiplication, division, remainder
           **+ -** addition, subtraction
           **< < >>  **left and right bitwise shifts
           **< = >= < >**
                  comparison
           **== !=** equality and inequality
           **&      **bitwise AND
           **^** bitwise exclusive OR
           **|** bitwise OR
           **& &     **logical AND
           **||** logical OR
           _expr_**?**_expr_**:**_expr_
                  conditional operator
           **= *= /= %= += -= <<= >>= &= ^= |=**
                  assignment
           _expr1_ **,**_expr2_
                  comma
    
           Shell variables are allowed as operands; parameter expansion is
           performed before the expression is evaluated.  Within an
           expression, shell variables may also be referenced by name without
           using the parameter expansion syntax.  This means you can use "x",
           where _x_ is a shell variable name, in an arithmetic expression, and
           the shell will evaluate its value as an expression and use the
           result.  A shell variable that is null or unset evaluates to 0
           when referenced by name in an expression.
    
           The value of a variable is evaluated as an arithmetic expression
           when it is referenced, or when a variable which has been given the
           _integer_ attribute using **declare -i** is assigned a value.  A null
           value evaluates to 0.  A shell variable need not have its _integer_
           attribute turned on to be used in an expression.
    
           Integer constants follow the C language definition, without
           suffixes or character constants.  Constants with a leading 0 are
           interpreted as octal numbers.  A leading 0x or 0X denotes
           hexadecimal.  Otherwise, numbers take the form [_base#_]n, where the
           optional _base_ is a decimal number between 2 and 64 representing
           the arithmetic base, and _n_ is a number in that base.  If _base#_ is
           omitted, then base 10 is used.  When specifying _n_ , if a non-digit
           is required, the digits greater than 9 are represented by the
           lowercase letters, the uppercase letters, @, and _, in that order.
           If _base_ is less than or equal to 36, lowercase and uppercase
           letters may be used interchangeably to represent numbers between
           10 and 35.
    
           Operators are evaluated in precedence order.  Sub-expressions in
           parentheses are evaluated first and may override the precedence
           rules above.
    


## CONDITIONAL EXPRESSIONS



           Conditional expressions are used by the **[[** compound command and
           the **test** and **[** builtin commands to test file attributes and
           perform string and arithmetic comparisons.  The **test** and **[**
           commands determine their behavior based on the number of
           arguments; see the descriptions of those commands for any other
           command-specific actions.
    
           Expressions are formed from the unary or binary primaries listed
           below.  Unary expressions are often used to examine the status of
           a file or shell variable.  Binary operators are used for string,
           numeric, and file attribute comparisons.
    
           **Bash** handles several filenames specially when they are used in
           expressions.  If the operating system on which **bash** is running
           provides these special files, bash will use them; otherwise it
           will emulate them internally with this behavior: If any _file_
           argument to one of the primaries is of the form _/dev/fd/n_ , then
           **bash** checks file descriptor _n_.  If the _file_ argument to one of the
           primaries is one of _/dev/stdin_ , _/dev/stdout_ , or _/dev/stderr_ , **bash**
           checks file descriptor 0, 1, or 2, respectively.
    
           Unless otherwise specified, primaries that operate on files follow
           symbolic links and operate on the target of the link, rather than
           the link itself.
    
           When used with **[[** , or when the shell is in posix mode, the **< **and **>**
           operators sort lexicographically using the current locale.  When
           the shell is not in posix mode, the **test** command sorts using ASCII
           ordering.
    
           **-a** _file_
                  True if _file_ exists.
           **-b** _file_
                  True if _file_ exists and is a block special file.
           **-c** _file_
                  True if _file_ exists and is a character special file.
           **-d** _file_
                  True if _file_ exists and is a directory.
           **-e** _file_
                  True if _file_ exists.
           **-f** _file_
                  True if _file_ exists and is a regular file.
           **-g** _file_
                  True if _file_ exists and is set-group-id.
           **-h** _file_
                  True if _file_ exists and is a symbolic link.
           **-k** _file_
                  True if _file_ exists and its “sticky” bit is set.
           **-p** _file_
                  True if _file_ exists and is a named pipe (FIFO).
           **-r** _file_
                  True if _file_ exists and is readable.
           **-s** _file_
                  True if _file_ exists and has a size greater than zero.
           **-t** _fd_  True if file descriptor _fd_ is open and refers to a
                  terminal.
           **-u** _file_
                  True if _file_ exists and its set-user-id bit is set.
           **-w** _file_
                  True if _file_ exists and is writable.
           **-x** _file_
                  True if _file_ exists and is executable.
           **-G** _file_
                  True if _file_ exists and is owned by the effective group id.
           **-L** _file_
                  True if _file_ exists and is a symbolic link.
           **-N** _file_
                  True if _file_ exists and has been modified since it was last
                  accessed.
           **-O** _file_
                  True if _file_ exists and is owned by the effective user id.
           **-S** _file_
                  True if _file_ exists and is a socket.
           **-o** _optname_
                  True if the shell option _optname_ is enabled.  See the list
                  of options under the description of the **-o** option to the
                  **set** builtin below.
           **-v** _varname_
                  True if the shell variable _varname_ is set (has been
                  assigned a value).  If _varname_ is an indexed array variable
                  name subscripted by _@_ or _*_ , this returns true if the array
                  has any set elements.  If _varname_ is an associative array
                  variable name subscripted by _@_ or _*_ , this returns true if
                  an element with that key is set.
           **-R** _varname_
                  True if the shell variable _varname_ is set and is a name
                  reference.
           **-z** _string_
                  True if the length of _string_ is zero.
           _string_
           **-n** _string_
                  True if the length of _string_ is non-zero.
    
           _string1_ **==**_string2_
           _string1_ **=**_string2_
                  True if the strings are equal.  **=** should be used with the
                  **test** command for POSIX conformance.  When used with the **[[**
                  command, this performs pattern matching as described above
                  (**Compound Commands**).
           _string1_ **!=**_string2_
                  True if the strings are not equal.
           _string1_ **< **_string2_
                  True if _string1_ sorts before _string2_ lexicographically.
           _string1_ **> **_string2_
                  True if _string1_ sorts after _string2_ lexicographically.
    
           _file1_ **-ef** _file2_
                  True if _file1_ and _file2_ refer to the same device and inode
                  numbers.
           _file1_ -**nt** _file2_
                  True if _file1_ is newer (according to modification date)
                  than _file2_ , or if _file1_ exists and _file2_ does not.
           _file1_ -**ot** _file2_
                  True if _file1_ is older than _file2_ , or if _file2_ exists and
                  _file1_ does not.
    
           _arg1_ **OP** _arg2_
                  **OP** is one of **-eq** , **-ne** , **-lt** , **-le** , **-gt** , or **-ge**.  These
                  arithmetic binary operators return true if _arg1_ is equal
                  to, not equal to, less than, less than or equal to, greater
                  than, or greater than or equal to _arg2_ , respectively.  _arg1_
                  and _arg2_ may be positive or negative integers.  When used
                  with the **[[** command, _arg1_ and _arg2_ are evaluated as
                  arithmetic expressions (see **ARITHMETIC EVALUATION** above).
                  Since the expansions the **[[** command performs on _arg1_ and
                  _arg2_ can potentially result in empty strings, arithmetic
                  expression evaluation treats those as expressions that
                  evaluate to 0.
    


## SIMPLE COMMAND EXPANSION



           When the shell executes a simple command, it performs the
           following expansions, assignments, and redirections, from left to
           right, in the following order.
    
           1.     The words that the parser has marked as variable
                  assignments (those preceding the command name) and
                  redirections are saved for later processing.
    
           2.     The words that are not variable assignments or redirections
                  are expanded.  If any words remain after expansion, the
                  first word is taken to be the name of the command and the
                  remaining words are the arguments.
    
           3.     Redirections are performed as described above under
                  **REDIRECTION**.
    
           4.     The text after the **=** in each variable assignment undergoes
                  tilde expansion, parameter expansion, command substitution,
                  arithmetic expansion, and quote removal before being
                  assigned to the variable.
    
           If no command name results, the variable assignments affect the
           current shell environment.  In the case of such a command (one
           that consists only of assignment statements and redirections),
           assignment statements are performed before redirections.
           Otherwise, the variables are added to the environment of the
           executed command and do not affect the current shell environment.
           If any of the assignments attempts to assign a value to a readonly
           variable, an error occurs, and the command exits with a non-zero
           status.
    
           If no command name results, redirections are performed, but do not
           affect the current shell environment.  A redirection error causes
           the command to exit with a non-zero status.
    
           If there is a command name left after expansion, execution
           proceeds as described below.  Otherwise, the command exits.  If
           one of the expansions contained a command substitution, the exit
           status of the command is the exit status of the last command
           substitution performed.  If there were no command substitutions,
           the command exits with a zero status.
    


## COMMAND EXECUTION



           After a command has been split into words, if it results in a
           simple command and an optional list of arguments, the shell
           performs the following actions.
    
           If the command name contains no slashes, the shell attempts to
           locate it.  If there exists a shell function by that name, that
           function is invoked as described above in **FUNCTIONS**.  If the name
           does not match a function, the shell searches for it in the list
           of shell builtins.  If a match is found, that builtin is invoked.
    
           If the name is neither a shell function nor a builtin, and
           contains no slashes, **bash** searches each element of the **PATH** for a
           directory containing an executable file by that name.  **Bash** uses a
           hash table to remember the full pathnames of executable files (see
           **hash** under **SHELL BUILTIN COMMANDS** below).  Bash performs a full
           search of the directories in **PATH** only if the command is not found
           in the hash table.  If the search is unsuccessful, the shell
           searches for a defined shell function named
           **command_not_found_handle**.  If that function exists, it is invoked
           in a separate execution environment with the original command and
           the original command's arguments as its arguments, and the
           function's exit status becomes the exit status of that subshell.
           If that function is not defined, the shell prints an error message
           and returns an exit status of 127.
    
           If the search is successful, or if the command name contains one
           or more slashes, the shell executes the named program in a
           separate execution environment.  Argument 0 is set to the name
           given, and the remaining arguments to the command are set to the
           arguments given, if any.
    
           If this execution fails because the file is not in executable
           format, and the file is not a directory, it is assumed to be a
           _shell script_ , a file containing shell commands, and the shell
           creates a new instance of itself to execute it.  Bash tries to
           determine whether the file is a text file or a binary, and will
           not execute files it determines to be binaries.  This subshell
           reinitializes itself, so that the effect is as if a new shell had
           been invoked to handle the script, with the exception that the
           locations of commands remembered by the parent (see **hash** below
           under **SHELL BUILTIN COMMANDS** are retained by the child.
    
           If the program is a file beginning with **#!** , the remainder of the
           first line specifies an interpreter for the program.  The shell
           executes the specified interpreter on operating systems that do
           not handle this executable format themselves.  The arguments to
           the interpreter consist of a single optional argument following
           the interpreter name on the first line of the program, followed by
           the name of the program, followed by the command arguments, if
           any.
    


## COMMAND EXECUTION ENVIRONMENT



           The shell has an _execution environment_ , which consists of the
           following:
    
           •      Open files inherited by the shell at invocation, as
                  modified by redirections supplied to the **exec** builtin.
    
           •      The current working directory as set by **cd** , **pushd** , or **popd** ,
                  or inherited by the shell at invocation.
    
           •      The file creation mode mask as set by **umask** or inherited
                  from the shell's parent.
    
           •      Current traps set by **trap**.
    
           •      Shell parameters that are set by variable assignment or
                  with **set** or inherited from the shell's parent in the
                  environment.
    
           •      Shell functions defined during execution or inherited from
                  the shell's parent in the environment.
    
           •      Options enabled at invocation (either by default or with
                  command-line arguments) or by **set**.
    
           •      Options enabled by **shopt**.
    
           •      Shell aliases defined with **alias**.
    
           •      Various process IDs, including those of background jobs,
                  the value of **$$** , and the value of **PPID**.
    
           When a simple command other than a builtin or shell function is to
           be executed, it is invoked in a separate execution environment
           that consists of the following.  Unless otherwise noted, the
           values are inherited from the shell.
    
           •      The shell's open files, plus any modifications and
                  additions specified by redirections to the command.
    
           •      The current working directory.
    
           •      The file creation mode mask.
    
           •      Shell variables and functions marked for export, along with
                  variables exported for the command, passed in the
                  environment.
    
           •      Traps caught by the shell are reset to the values inherited
                  from the shell's parent, and traps ignored by the shell are
                  ignored.
    
           A command invoked in this separate environment cannot affect the
           shell's execution environment.
    
           A _subshell_ is a copy of the shell process.
    
           Command substitution, commands grouped with parentheses, and
           asynchronous commands are invoked in a subshell environment that
           is a duplicate of the shell environment, except that traps caught
           by the shell are reset to the values that the shell inherited from
           its parent at invocation.  Builtin commands that are invoked as
           part of a pipeline, except possibly in the last element depending
           on the value of the **lastpipe** shell option, are also executed in a
           subshell environment.  Changes made to the subshell environment
           cannot affect the shell's execution environment.
    
           When the shell is in posix mode, subshells spawned to execute
           command substitutions inherit the value of the **-e** option from
           their parent shell.  When not in posix mode, **bash** clears the **-e**
           option in such subshells.  See the description of the
           **inherit_errexit** shell option below for how to control this
           behavior when not in posix mode.
    
           If a command is followed by a **& **and job control is not active, the
           default standard input for the command is the empty file
           _/dev/null_.  Otherwise, the invoked command inherits the file
           descriptors of the calling shell as modified by redirections.
    


## ENVIRONMENT



           When a program is invoked it is given an array of strings called
           the _environment_.  This is a list of _name_ -_value_ pairs, of the form
           _name_ =_value_.
    
           The shell provides several ways to manipulate the environment.  On
           invocation, the shell scans its own environment and creates a
           parameter for each name found, automatically marking it for _export_
           to child processes.  Executed commands inherit the environment.
           The **export** , **declare -x** , and **unset** commands modify the environment
           by adding and deleting parameters and functions.  If the value of
           a parameter in the environment is modified, the new value
           automatically becomes part of the environment, replacing the old.
           The environment inherited by any executed command consists of the
           shell's initial environment, whose values may be modified in the
           shell, less any pairs removed by the **unset** or **export -n** commands,
           plus any additions via the **export** and **declare -x** commands.
    
           If any parameter assignments, as described above in **PARAMETERS** ,
           appear before a _simple command_ , the variable assignments are part
           of that command's environment for as long as it executes.  These
           assignment statements affect only the environment seen by that
           command.  If these assignments precede a call to a shell function,
           the variables are local to the function and exported to that
           function's children.
    
           If the **-k** option is set (see the **set** builtin command below), then
           _all_ parameter assignments are placed in the environment for a
           command, not just those that precede the command name.
    
           When **bash** invokes an external command, the variable **_** is set to
           the full pathname of the command and passed to that command in its
           environment.
    


## EXIT STATUS



           The exit status of an executed command is the value returned by
           the _waitpid_ system call or equivalent function.  Exit statuses
           fall between 0 and 255, though, as explained below, the shell may
           use values above 125 specially.  Exit statuses from shell builtins
           and compound commands are also limited to this range.  Under
           certain circumstances, the shell will use special values to
           indicate specific failure modes.
    
           For the shell's purposes, a command which exits with a zero exit
           status has succeeded.  So while an exit status of zero indicates
           success, a non-zero exit status indicates failure.
    
           When a command terminates on a fatal signal _N_ , **bash** uses the value
           of 128+_N_ as the exit status.
    
           If a command is not found, the child process created to execute it
           returns a status of 127.  If a command is found but is not
           executable, the return status is 126.
    
           If a command fails because of an error during expansion or
           redirection, the exit status is greater than zero.
    
           Shell builtin commands return a status of 0 (_true_) if successful,
           and non-zero (_false_) if an error occurs while they execute.  All
           builtins return an exit status of 2 to indicate incorrect usage,
           generally invalid options or missing arguments.
    
           The exit status of the last command is available in the special
           parameter $?.
    
           **Bash** itself returns the exit status of the last command executed,
           unless a syntax error occurs, in which case it exits with a non-
           zero value.  See also the **exit** builtin command below.
    


## SIGNALS



           When **bash** is interactive, in the absence of any traps, it ignores
           **SIGTERM**(so that **kill 0** does not kill an interactive shell), and
           catches and handles **SIGINT**(so that the **wait** builtin is
           interruptible).  When **bash** receives **SIGINT** , it breaks out of any
           executing loops.  In all cases, **bash** ignores **SIGQUIT**.  If job
           control is in effect, **bash** ignores **SIGTTIN** , **SIGTTOU** , and **SIGTSTP**.
    
           The **trap** builtin modifies the shell's signal handling, as
           described below.
    
           Non-builtin commands **bash** executes have signal handlers set to the
           values inherited by the shell from its parent, unless **trap** sets
           them to be ignored, in which case the child process will ignore
           them as well.  When job control is not in effect, asynchronous
           commands ignore **SIGINT** and **SIGQUIT** in addition to these inherited
           handlers.  Commands run as a result of command substitution ignore
           the keyboard-generated job control signals **SIGTTIN** , **SIGTTOU** , and
           **SIGTSTP**.
    
           The shell exits by default upon receipt of a **SIGHUP**.  Before
           exiting, an interactive shell resends the **SIGHUP** to all jobs,
           running or stopped.  The shell sends **SIGCONT** to stopped jobs to
           ensure that they receive the **SIGHUP**(see **JOB CONTROL** below for
           more information about running and stopped jobs).  To prevent the
           shell from sending the signal to a particular job, remove it from
           the jobs table with the **disown** builtin (see **SHELL BUILTIN COMMANDS**
           below) or mark it not to receive **SIGHUP** using **disown -h**.
    
           If the **huponexit** shell option has been set using **shopt** , **bash** sends
           a **SIGHUP** to all jobs when an interactive login shell exits.
    
           If **bash** is waiting for a command to complete and receives a signal
           for which a trap has been set, it will not execute the trap until
           the command completes.  If **bash** is waiting for an asynchronous
           command via the **wait** builtin, and it receives a signal for which a
           trap has been set, the **wait** builtin will return immediately with
           an exit status greater than 128, immediately after which the shell
           executes the trap.
    
           When job control is not enabled, and **bash** is waiting for a
           foreground command to complete, the shell receives keyboard-
           generated signals such as **SIGINT**(usually generated by **^C**) that
           users commonly intend to send to that command.  This happens
           because the shell and the command are in the same process group as
           the terminal, and **^C** sends **SIGINT** to all processes in that process
           group.  Since **bash** does not enable job control by default when the
           shell is not interactive, this scenario is most common in non-
           interactive shells.
    
           When job control is enabled, and **bash** is waiting for a foreground
           command to complete, the shell does not receive keyboard-generated
           signals, because it is not in the same process group as the
           terminal.  This scenario is most common in interactive shells,
           where **bash** attempts to enable job control by default.  See **JOB**
           **CONTROL** below for more information about process groups.
    
           When job control is not enabled, and **bash** receives **SIGINT** while
           waiting for a foreground command, it waits until that foreground
           command terminates and then decides what to do about the **SIGINT** :
    
           1.     If the command terminates due to the **SIGINT** , **bash** concludes
                  that the user meant to send the **SIGINT** to the shell as
                  well, and acts on the **SIGINT**(e.g., by running a **SIGINT**
                  trap, exiting a non-interactive shell, or returning to the
                  top level to read a new command).
    
           2.     If the command does not terminate due to **SIGINT** , the
                  program handled the **SIGINT** itself and did not treat it as a
                  fatal signal.  In that case, **bash** does not treat **SIGINT** as
                  a fatal signal, either, instead assuming that the **SIGINT**
                  was used as part of the program's normal operation (e.g.,
                  emacs uses it to abort editing commands) or deliberately
                  discarded.  However, **bash** will run any trap set on **SIGINT** ,
                  as it does with any other trapped signal it receives while
                  it is waiting for the foreground command to complete, for
                  compatibility.
    
           When job control is enabled, **bash** does not receive keyboard-
           generated signals such as **SIGINT** while it is waiting for a
           foreground command.  An interactive shell does not pay attention
           to the **SIGINT** , even if the foreground command terminates as a
           result, other than noting its exit status.  If the shell is not
           interactive, and the foreground command terminates due to the
           **SIGINT** , **bash** pretends it received the **SIGINT** itself (scenario 1
           above), for compatibility.
    


## JOB CONTROL



           _Job control_ refers to the ability to selectively stop (_suspend_)
           the execution of processes and continue (_resume_) their execution
           at a later point.  A user typically employs this facility via an
           interactive interface supplied jointly by the operating system
           kernel's terminal driver and **bash**.
    
           The shell associates a _job_ with each pipeline.  It keeps a table
           of currently executing jobs, which the **jobs** command will display.
           Each job has a _job number_ , which **jobs** displays between brackets.
           Job numbers start at 1.  When **bash** starts a job asynchronously (in
           the _background_), it prints a line that looks like:
    
                  [1] 25647
    
           indicating that this job is job number 1 and that the process ID
           of the last process in the pipeline associated with this job is
           25647.  All of the processes in a single pipeline are members of
           the same job.  **Bash** uses the _job_ abstraction as the basis for job
           control.
    
           To facilitate the implementation of the user interface to job
           control, each process has a _process group ID_ , and the operating
           system maintains the notion of a _current terminal process group_
           _ID_.  This terminal process group ID is associated with the
           _controlling terminal_.
    
           Processes that have the same process group ID are said to be part
           of the same _process group_.  Members of the _foreground_ process
           group (processes whose process group ID is equal to the current
           terminal process group ID) receive keyboard-generated signals such
           as **SIGINT**.  Processes in the foreground process group are said to
           be _foreground_ processes.  _Background_ processes are those whose
           process group ID differs from the controlling terminal's; such
           processes are immune to keyboard-generated signals.  Only
           foreground processes are allowed to read from or, if the user so
           specifies with “stty tostop”, write to the controlling terminal.
           The system sends a **SIGTTIN (SIGTTOU)** signal to background
           processes which attempt to read from (write to when “tostop” is in
           effect) the terminal, which, unless caught, suspends the process.
    
           If the operating system on which **bash** is running supports job
           control, **bash** contains facilities to use it.  Typing the _suspend_
           character (typically **^Z** , Control-Z) while a process is running
           stops that process and returns control to **bash**.  Typing the
           _delayed suspend_ character (typically **^Y** , Control-Y) causes the
           process stop when it attempts to read input from the terminal, and
           returns control to **bash**.  The user then manipulates the state of
           this job, using the **bg** command to continue it in the background,
           the **fg** command to continue it in the foreground, or the **kill**
           command to kill it.  The suspend character takes effect
           immediately, and has the additional side effect of discarding any
           pending output and typeahead.  To force a background process to
           stop, or stop a process that's not associated with the current
           terminal session, send it the **SIGSTOP** signal using **kill**.
    
           There are a number of ways to refer to a job in the shell.  The **%**
           character introduces a job specification (jobspec).
    
           Job number _n_ may be referred to as **%n**.  A job may also be referred
           to using a prefix of the name used to start it, or using a
           substring that appears in its command line.  For example, **%ce**
           refers to a job whose command name begins with **ce**.  Using **%?ce** , on
           the other hand, refers to any job containing the string **ce** in its
           command line.  If the prefix or substring matches more than one
           job, **bash** reports an error.
    
           The symbols **%%** and **%+** refer to the shell's notion of the _current_
           _job_.  A single % (with no accompanying job specification) also
           refers to the current job.  **%-** refers to the _previous job_.  When a
           job starts in the background, a job stops while in the foreground,
           or a job is resumed in the background, it becomes the current job.
           The job that was the current job becomes the previous job.  When
           the current job terminates, the previous job becomes the current
           job.  If there is only a single job, **%+** and **%-** can both be used to
           refer to that job.  In output pertaining to jobs (e.g., the output
           of the **jobs** command), the current job is always marked with a **+** ,
           and the previous job with a **-**.
    
           Simply naming a job can be used to bring it into the foreground:
           **%1** is a synonym for “fg %1”, bringing job 1 from the background
           into the foreground.  Similarly, “%1 &” resumes job 1 in the
           background, equivalent to “bg %1”.
    
           The shell learns immediately whenever a job changes state.
           Normally, **bash** waits until it is about to print a prompt before
           notifying the user about changes in a job's status so as to not
           interrupt any other output, though it will notify of changes in a
           job's status after a foreground command in a list completes,
           before executing the next command in the list.  If the **-b** option
           to the **set** builtin command is enabled, **bash** reports status changes
           immediately.  **Bash** executes any trap on **SIGCHLD** for each child
           that terminates.
    
           When a job terminates and **bash** notifies the user about it, **bash**
           removes the job from the table.  It will not appear in **jobs**
           output, but **wait** will report its exit status, as long as it's
           supplied the process ID associated with the job as an argument.
           When the table is empty, job numbers start over at 1.
    
           If a user attempts to exit **bash** while jobs are stopped (or, if the
           **checkjobs** shell option has been enabled using the **shopt** builtin,
           running), the shell prints a warning message, and, if the
           **checkjobs** option is enabled, lists the jobs and their statuses.
           The **jobs** command may then be used to inspect their status.  If the
           user immediately attempts to exit again, without an intervening
           command, **bash** does not print another warning, and terminates any
           stopped jobs.
    
           When the shell is waiting for a job or process using the **wait**
           builtin, and job control is enabled, **wait** will return when the job
           changes state.  The **-f** option causes **wait** to wait until the job or
           process terminates before returning.
    


## PROMPTING



           When executing interactively, **bash** displays the primary prompt **PS1**
           when it is ready to read a command, and the secondary prompt **PS2**
           when it needs more input to complete a command.
    
           **Bash** examines the value of the array variable **PROMPT_COMMAND** just
           before printing each primary prompt.  If any elements in
           **PROMPT_COMMAND** are set and non-null, Bash executes each value, in
           numeric order, just as if it had been typed on the command line.
           **Bash** displays **PS0** after it reads a command but before executing
           it.
    
           **Bash** displays **PS4** as described above before tracing each command
           when the **-x** option is enabled.
    
           **Bash** allows the prompt strings **PS0** , **PS1** , **PS2** , and **PS4** , to be
           customized by inserting a number of backslash-escaped special
           characters that are decoded as follows:
    
                  **\a** An ASCII bell character (07).
                  **\d** The date in “Weekday Month Date” format (e.g., “Tue
                         May 26”).
                  **\D{**_format_**}**
                         The _format_ is passed to strftime(3) and the result
                         is inserted into the prompt string; an empty _format_
                         results in a locale-specific time representation.
                         The braces are required.
                  **\e** An ASCII escape character (033).
                  **\h** The hostname up to the first “.”.
                  **\H** The hostname.
                  **\j** The number of jobs currently managed by the shell.
                  **\l** The basename of the shell's terminal device name
                         (e.g., “ttys0”).
                  **\n** A newline.
                  **\r** A carriage return.
                  **\s** The name of the shell: the basename of **$0**(the
                         portion following the final slash).
                  **\t** The current time in 24-hour HH:MM:SS format.
                  **\T** The current time in 12-hour HH:MM:SS format.
                  **\@** The current time in 12-hour am/pm format.
                  **\A** The current time in 24-hour HH:MM format.
                  **\u** The username of the current user.
                  **\v** The **bash** version (e.g., 2.00).
                  **\V** The **bash** release, version + patch level (e.g.,
                         2.00.0)
                  **\w** The value of the **PWD** shell variable (**$PWD**), with
                         **$HOME** abbreviated with a tilde (uses the value of
                         the **PROMPT_DIRTRIM** variable).
                  **\W** The basename of **$PWD** , with **$HOME** abbreviated with a
                         tilde.
                  **\!** The history number of this command.
                  **\#** The command number of this command.
                  **\$** If the effective UID is 0, a **#** , otherwise a **$**.
                  **\**_nnn_   The character corresponding to the octal number _nnn_.
                  **\\** A backslash.
                  **\[** Begin a sequence of non-printing characters, which
                         could be used to embed a terminal control sequence
                         into the prompt.
                  **\]** End a sequence of non-printing characters.
    
           The command number and the history number are usually different:
           the history number of a command is its position in the history
           list, which may include commands restored from the history file
           (see **HISTORY** below), while the command number is the position in
           the sequence of commands executed during the current shell
           session.  After the string is decoded, it is expanded via
           parameter expansion, command substitution, arithmetic expansion,
           and quote removal, subject to the value of the **promptvars** shell
           option (see the description of the **shopt** command under **SHELL**
           **BUILTIN COMMANDS** below).  This can have unwanted side effects if
           escaped portions of the string appear within command substitution
           or contain characters special to word expansion.
    


## READLINE



           This is the library that handles reading input when using an
           interactive shell, unless the **--noediting** option is supplied at
           shell invocation.  Line editing is also used when using the **-e**
           option to the **read** builtin.  By default, the line editing commands
           are similar to those of emacs; a vi-style line editing interface
           is also available.  Line editing can be enabled at any time using
           the **-o emacs** or **-o vi** options to the **set** builtin (see **SHELL**
           **BUILTIN COMMANDS** below).  To turn off line editing after the shell
           is running, use the **+o emacs** or **+o vi** options to the **set** builtin.
    
       **Readline Notation**
           This section uses Emacs-style editing concepts and uses its
           notation for keystrokes.  Control keys are denoted by C-_key_ , e.g.,
           C-n means Control-N.  Similarly, _meta_ keys are denoted by M-_key_ ,
           so M-x means Meta-X.  The Meta key is often labeled “Alt” or
           “Option”.
    
           On keyboards without a _Meta_ key, M-_x_ means ESC _x_ , i.e., press and
           release the Escape key, then press and release the _x_ key, in
           sequence.  This makes ESC the _meta prefix_.  The combination M-C-_x_
           means ESC Control-_x_ : press and release the Escape key, then press
           and hold the Control key while pressing the _x_ key, then release
           both.
    
           On some keyboards, the Meta key modifier produces characters with
           the eighth bit (0200) set.  You can use the **enable-meta-key**
           variable to control whether or not it does this, if the keyboard
           allows it.  On many others, the terminal or terminal emulator
           converts the metafied key to a key sequence beginning with ESC as
           described in the preceding paragraph.
    
           If your _Meta_ key produces a key sequence with the ESC meta prefix,
           you can make M-_key_ key bindings you specify (see **Readline Key**
           **Bindings** below) do the same thing by setting the **force-meta-prefix**
           variable.
    
           **Readline** commands may be given numeric _arguments_ , which normally
           act as a repeat count.  Sometimes, however, it is the sign of the
           argument that is significant.  Passing a negative argument to a
           command that acts in the forward direction (e.g., **kill-line**) makes
           that command act in a backward direction.  Commands whose behavior
           with arguments deviates from this are noted below.
    
           The _point_ is the current cursor position, and _mark_ refers to a
           saved cursor position.  The text between the point and mark is
           referred to as the _region_.  **Readline** has the concept of an _active_
           _region_ : when the region is active, **readline** redisplay highlights
           the region using the value of the **active-region-start-color**
           variable.  The **enable-active-region** variable turns this on and
           off.  Several commands set the region to active; those are noted
           below.
    
           When a command is described as _killing_ text, the text deleted is
           saved for possible future retrieval (_yanking_).  The killed text is
           saved in a _kill ring_.  Consecutive kills accumulate the deleted
           text into one unit, which can be yanked all at once.  Commands
           which do not kill text separate the chunks of text on the kill
           ring.
    
       **Readline Initialization**
           **Readline** is customized by putting commands in an initialization
           file (the _inputrc_ file).  The name of this file is taken from the
           value of the **INPUTRC** shell variable.  If that variable is unset,
           the default is _~/.inputrc_.  If that file  does not exist or cannot
           be read, **readline** looks for _/etc/inputrc_.  When a program that
           uses the **readline** library starts up, **readline** reads the
           initialization file and sets the key bindings and variables found
           there, before reading any user input.
    
           There are only a few basic constructs allowed in the inputrc file.
           Blank lines are ignored.  Lines beginning with a **#** are comments.
           Lines beginning with a **$** indicate conditional constructs.  Other
           lines denote key bindings and variable settings.
    
           The default key-bindings in this section may be changed using key
           binding commands in the _inputrc_ file.  Programs that use the
           **readline** library, including **bash** , may add their own commands and
           bindings.
    
           For example, placing
    
                  M-Control-u: universal-argument
           or
                  C-Meta-u: universal-argument
    
           into the _inputrc_ would make M-C-u execute the **readline** command
           _universal-argument_.
    
           Key bindings may contain the following symbolic character names:
           _DEL_ , _ESC_ , _ESCAPE_ , _LFD_ , _NEWLINE_ , _RET_ , _RETURN_ , _RUBOUT_ (a destructive
           backspace), _SPACE_ , _SPC_ , and _TAB_.
    
           In addition to command names, **readline** allows keys to be bound to
           a string that is inserted when the key is pressed (a _macro_).  The
           difference between a macro and a command is that a macro is
           enclosed in single or double quotes.
    
       **Readline Key Bindings**
           The syntax for controlling key bindings in the _inputrc_ file is
           simple.  All that is required is the name of the command or the
           text of a macro and a key sequence to which it should be bound.
           The key sequence may be specified in one of two ways: as a
           symbolic key name, possibly with _Meta-_ or _Control-_ prefixes, or as
           a key sequence composed of one or more characters enclosed in
           double quotes.  The key sequence and name are separated by a
           colon.  There can be no whitespace between the name and the colon.
    
           When using the form **keyname** :_function-name_ or _macro_ , _keyname_ is the
           name of a key spelled out in English.  For example:
    
                  Control-u: universal-argument
                  Meta-Rubout: backward-kill-word
                  Control-o: "> output"
    
           In the above example, _C-u_ is bound to the function
           **universal-argument** , _M-DEL_ is bound to the function
           **backward-kill-word** , and _C-o_ is bound to run the macro expressed on
           the right hand side (that is, to insert the text “> output” into
           the line).
    
           In the second form, **"keyseq"** :_function-name_ or _macro_ , **keyseq**
           differs from **keyname** above in that strings denoting an entire key
           sequence may be specified by placing the sequence within double
           quotes.  Some GNU Emacs style key escapes can be used, as in the
           following example, but none of the symbolic character names are
           recognized.
    
                  "\C-u": universal-argument
                  "\C-x\C-r": re-read-init-file
                  "\e[11~": "Function Key 1"
    
           In this example, _C-u_ is again bound to the function
           **universal-argument**.  _C-x C-r_ is bound to the function
           **re-read-init-file** , and _ESC [ 1 1 ~_ is bound to insert the text
           “Function Key 1”.
    
           The full set of GNU Emacs style escape sequences available when
           specifying key sequences is
                  **\C-** A control prefix.
                  **\M-** Adding the meta prefix or converting the following
                         character to a meta character, as described below
                         under **force-meta-prefix**.
                  **\e** An escape character.
                  **\\** Backslash.
                  **\"** Literal ", a double quote.
                  **\'** Literal ', a single quote.
    
           In addition to the GNU Emacs style escape sequences, a second set
           of backslash escapes is available:
                  **\a** alert (bell)
                  **\b** backspace
                  **\d** delete
                  **\f** form feed
                  **\n** newline
                  **\r** carriage return
                  **\t** horizontal tab
                  **\v** vertical tab
                  **\**_nnn_   The eight-bit character whose value is the octal
                         value _nnn_ (one to three digits).
                  **\x** _HH_   The eight-bit character whose value is the
                         hexadecimal value _HH_ (one or two hex digits).
    
           When entering the text of a macro, single or double quotes must be
           used to indicate a macro definition.  Unquoted text is assumed to
           be a function name.  The backslash escapes described above are
           expanded in the macro body.  Backslash quotes any other character
           in the macro text, including " and '.
    
           **Bash** will display or modify the current **readline** key bindings with
           the **bind** builtin command.  The **-o emacs** or **-o vi** options to the
           **set** builtin (see **SHELL BUILTIN COMMANDS** below) change the editing
           mode during interactive use.
    
       **Readline Variables**
           **Readline** has variables that can be used to further customize its
           behavior.  A variable may be set in the _inputrc_ file with a
           statement of the form
    
                  **set** _variable-name value_
           or using the **bind** builtin command (see **SHELL BUILTIN COMMANDS**
           below).
    
           Except where noted, **readline** variables can take the values **On** or
           **Off**(without regard to case).  Unrecognized variable names are
           ignored.  When **readline** reads a variable value, empty or null
           values, “on” (case-insensitive), and “1” are equivalent to **On**.
           All other values are equivalent to **Off**.
    
           The **bind -V** command lists the current **readline** variable names and
           values (see **SHELL BUILTIN COMMANDS** below).
    
           The variables and their default values are:
    
           **active-region-start-color**
                  A string variable that controls the text color and
                  background when displaying the text in the active region
                  (see the description of **enable-active-region** below).  This
                  string must not take up any physical character positions on
                  the display, so it should consist only of terminal escape
                  sequences.  It is output to the terminal before displaying
                  the text in the active region.  This variable is reset to
                  the default value whenever the terminal type changes.  The
                  default value is the string that puts the terminal in
                  standout mode, as obtained from the terminal's terminfo
                  description.  A sample value might be “\e[01;33m”.
           **active-region-end-color**
                  A string variable that “undoes” the effects of
                  **active-region-start-color** and restores “normal” terminal
                  display appearance after displaying text in the active
                  region.  This string must not take up any physical
                  character positions on the display, so it should consist
                  only of terminal escape sequences.  It is output to the
                  terminal after displaying the text in the active region.
                  This variable is reset to the default value whenever the
                  terminal type changes.  The default value is the string
                  that restores the terminal from standout mode, as obtained
                  from the terminal's terminfo description.  A sample value
                  might be “\e[0m”.
           **bell-style (audible)**
                  Controls what happens when **readline** wants to ring the
                  terminal bell.  If set to **none** , **readline** never rings the
                  bell.  If set to **visible** , **readline** uses a visible bell if
                  one is available.  If set to **audible** , **readline** attempts to
                  ring the terminal's bell.
           **bind-tty-special-chars (On)**
                  If set to **On** , **readline** attempts to bind the control
                  characters that are treated specially by the kernel's
                  terminal driver to their **readline** equivalents.  These
                  override the default **readline** bindings described here.
                  Type “stty -a” at a **bash** prompt to see your current
                  terminal settings, including the special control characters
                  (usually **cchars**).
           **blink-matching-paren (Off)**
                  If set to **On** , **readline** attempts to briefly move the cursor
                  to an opening parenthesis when a closing parenthesis is
                  inserted.
           **colored-completion-prefix (Off)**
                  If set to **On** , when listing completions, **readline** displays
                  the common prefix of the set of possible completions using
                  a different color.  The color definitions are taken from
                  the value of the **LS_COLORS** environment variable.  If there
                  is a color definition in **$LS_COLORS** for the custom suffix
                  “.readline-colored-completion-prefix”, **readline** uses this
                  color for the common prefix instead of its default.
           **colored-stats (Off)**
                  If set to **On** , **readline** displays possible completions using
                  different colors to indicate their file type.  The color
                  definitions are taken from the value of the **LS_COLORS**
                  environment variable.
           **comment-begin (** “**#** ”**)**
                  The string that the **readline insert-comment** command
                  inserts.  This command is bound to **M-#** in emacs mode and to
                  **#** in vi command mode.
           **completion-display-width (-1)**
                  The number of screen columns used to display possible
                  matches when performing completion.  The value is ignored
                  if it is less than 0 or greater than the terminal screen
                  width.  A value of 0 causes matches to be displayed one per
                  line.  The default value is -1.
           **completion-ignore-case (Off)**
                  If set to **On** , **readline** performs filename matching and
                  completion in a case-insensitive fashion.
           **completion-map-case (Off)**
                  If set to **On** , and **completion-ignore-case** is enabled,
                  **readline** treats hyphens (_-_) and underscores (___) as
                  equivalent when performing case-insensitive filename
                  matching and completion.
           **completion-prefix-display-length**(0)
                  The maximum length in characters of the common prefix of a
                  list of possible completions that is displayed without
                  modification.  When set to a value greater than zero,
                  **readline** replaces common prefixes longer than this value
                  with an ellipsis when displaying possible completions.  If
                  a completion begins with a period, and **eadline** is
                  completing filenames, it uses three underscores instead of
                  an ellipsis.
           **completion-query-items (100)**
                  This determines when the user is queried about viewing the
                  number of possible completions generated by the
                  **possible-completions** command.  It may be set to any integer
                  value greater than or equal to zero.  If the number of
                  possible completions is greater than or equal to the value
                  of this variable, **readline** asks whether or not the user
                  wishes to view them; otherwise **readline** simply lists them
                  on the terminal.  A zero value means **readline** should never
                  ask; negative values are treated as zero.
           **convert-meta (On)**
                  If set to **On** , **readline** converts characters it reads that
                  have the eighth bit set to an ASCII key sequence by
                  clearing the eighth bit and prefixing it with an escape
                  character (converting the character to have the meta
                  prefix).  The default is _On_ , but **readline** sets it to _Off_ if
                  the locale contains characters whose encodings may include
                  bytes with the eighth bit set.  This variable is dependent
                  on the **LC_CTYPE** locale category, and may change if the
                  locale changes.  This variable also affects key bindings;
                  see the description of **force-meta-prefix** below.
           **disable-completion (Off)**
                  If set to **On** , **readline** inhibits word completion.
                  Completion characters are inserted into the line as if they
                  had been mapped to **self-insert**.
           **echo-control-characters (On)**
                  When set to **On** , on operating systems that indicate they
                  support it, **readline** echoes a character corresponding to a
                  signal generated from the keyboard.
           **editing-mode (emacs)**
                  Controls whether **readline** uses a set of key bindings
                  similar to _Emacs_ or _vi_.  **editing-mode** can be set to either
                  **emacs** or **vi**.
           **emacs-mode-string (@)**
                  If the _show-mode-in-prompt_ variable is enabled, this string
                  is displayed immediately before the last line of the
                  primary prompt when emacs editing mode is active.  The
                  value is expanded like a key binding, so the standard set
                  of meta- and control- prefixes and backslash escape
                  sequences is available.  The \1 and \2 escapes begin and
                  end sequences of non-printing characters, which can be used
                  to embed a terminal control sequence into the mode string.
           **enable-active-region (On)**
                  When this variable is set to _On_ , **readline** allows certain
                  commands to designate the region as _active_.  When the
                  region is active, **readline** highlights the text in the
                  region using the value of the **active-region-start-color**
                  variable, which defaults to the string that enables the
                  terminal's standout mode.  The active region shows the text
                  inserted by bracketed-paste and any matching text found by
                  incremental and non-incremental history searches.
           **enable-bracketed-paste (On)**
                  When set to **On** , **readline** configures the terminal to insert
                  each paste into the editing buffer as a single string of
                  characters, instead of treating each character as if it had
                  been read from the keyboard.  This is called
                  _bracketed-paste mode_ ; it prevents **readline** from executing
                  any editing commands bound to key sequences appearing in
                  the pasted text.
           **enable-keypad (Off)**
                  When set to **On** , **readline** tries  to enable the application
                  keypad when it is called.  Some systems need this to enable
                  the arrow keys.
           **enable-meta-key (On)**
                  When set to **On** , **readline** tries to enable any meta modifier
                  key the terminal claims to support.  On many terminals, the
                  Meta key is used to send eight-bit characters; this
                  variable checks for the terminal capability that indicates
                  the terminal can enable and disable a mode that sets the
                  eighth bit of a character (0200) if the Meta key is held
                  down when the character is typed (a meta character).
           **expand-tilde (Off)**
                  If set to **On** , **readline** performs tilde expansion when it
                  attempts word completion.
           **force-meta-prefix (Off)**
                  If set to **On** , **readline** modifies its behavior when binding
                  key sequences containing \M- or Meta- (see **Key Bindings**
                  above) by converting a key sequence of the form \M-_C_ or
                  Meta-_C_ to the two-character sequence **ESC** _C_ (adding the meta
                  prefix).  If **force-meta-prefix** is set to **Off**(the default),
                  **readline** uses the value of the **convert-meta** variable to
                  determine whether to perform this conversion: if
                  **convert-meta** is **On** , **readline** performs the conversion
                  described above; if it is **Off** , **readline** converts _C_ to a
                  meta character by setting the eighth bit (0200).
           **history-preserve-point (Off)**
                  If set to **On** , the history code attempts to place point at
                  the same location on each history line retrieved with
                  **previous-history** or **next-history**.
           **history-size (unset)**
                  Set the maximum number of history entries saved in the
                  history list.  If set to zero, any existing history entries
                  are deleted and no new entries are saved.  If set to a
                  value less than zero, the number of history entries is not
                  limited.  By default, **bash** sets the maximum number of
                  history entries to the value of the **HISTSIZE** shell
                  variable.  Setting _history-size_ to a non-numeric value will
                  set the maximum number of history entries to 500.
           **horizontal-scroll-mode (Off)**
                  Setting this variable to **On** makes **readline** use a single
                  line for display, scrolling the input horizontally on a
                  single screen line when it becomes longer than the screen
                  width rather than wrapping to a new line.  This setting is
                  automatically enabled for terminals of height 1.
           **input-meta (Off)**
                  If set to **On** , **readline** enables eight-bit input (that is, it
                  does not clear the eighth bit in the characters it reads),
                  regardless of what the terminal claims it can support.  The
                  default is _Off_ , but **readline** sets it to _On_ if the locale
                  contains characters whose encodings may include bytes with
                  the eighth bit set.  This variable is dependent on the
                  **LC_CTYPE** locale category, and its value may change if the
                  locale changes.  The name **meta-flag** is a synonym for
                  **input-meta**.
           **isearch-terminators (** “**C-[C-j** ”**)**
                  The string of characters that should terminate an
                  incremental search without subsequently executing the
                  character as a command.  If this variable has not been
                  given a value, the characters _ESC_ and **C-j** terminate an
                  incremental search.
           **keymap (emacs)**
                  Set the current **readline** keymap.  The set of valid keymap
                  names is _emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,_
                  _vi-command_ , and _vi-insert_.  _vi_ is equivalent to _vi-command_ ;
                  _emacs_ is equivalent to _emacs-standard_.  The default value
                  is _emacs_ ; the value of **editing-mode** also affects the
                  default keymap.
           **keyseq-timeout (500)**
                  Specifies the duration **readline** will wait for a character
                  when reading an ambiguous key sequence (one that can form a
                  complete key sequence using the input read so far, or can
                  take additional input to complete a longer key sequence).
                  If **readline** does not receive any input within the timeout,
                  it uses the shorter but complete key sequence.  The value
                  is specified in milliseconds, so a value of 1000 means that
                  **readline** will wait one second for additional input.  If
                  this variable is set to a value less than or equal to zero,
                  or to a non-numeric value, **readline** waits until another key
                  is pressed to decide which key sequence to complete.
           **mark-directories (On)**
                  If set to **On** , completed directory names have a slash
                  appended.
           **mark-modified-lines (Off)**
                  If set to **On** , **readline** displays history lines that have
                  been modified with a preceding asterisk (*****).
           **mark-symlinked-directories (Off)**
                  If set to **On** , completed names which are symbolic links to
                  directories have a slash appended, subject to the value of
                  **mark-directories**.
           **match-hidden-files (On)**
                  This variable, when set to **On** , forces **readline** to match
                  files whose names begin with a “.”  (hidden files) when
                  performing filename completion.  If set to **Off** , the user
                  must include the leading “.”  in the filename to be
                  completed.
           **menu-complete-display-prefix (Off)**
                  If set to **On** , menu completion displays the common prefix of
                  the list of possible completions (which may be empty)
                  before cycling through the list.
           **output-meta (Off)**
                  If set to **On** , **readline** displays characters with the eighth
                  bit set directly rather than as a meta-prefixed escape
                  sequence.  The default is _Off_ , but **readline** sets it to _On_
                  if the locale contains characters whose encodings may
                  include bytes with the eighth bit set.  This variable is
                  dependent on the **LC_CTYPE** locale category, and its value
                  may change if the locale changes.
           **page-completions (On)**
                  If set to **On** , **readline** uses an internal pager resembling
                  more(1) to display a screenful of possible completions at a
                  time.
           **prefer-visible-bell**
                  See **bell-style**.
           **print-completions-horizontally (Off)**
                  If set to **On** , **readline** displays completions with matches
                  sorted horizontally in alphabetical order, rather than down
                  the screen.
           **revert-all-at-newline (Off)**
                  If set to **On** , **readline** will undo all changes to history
                  lines before returning when executing **accept-line**.  By
                  default, history lines may be modified and retain
                  individual undo lists across calls to **readline**.
           **search-ignore-case (Off)**
                  If set to **On** , **readline** performs incremental and non-
                  incremental history list searches in a case-insensitive
                  fashion.
           **show-all-if-ambiguous (Off)**
                  This alters the default behavior of the completion
                  functions.  If set to **On** , words which have more than one
                  possible completion cause the matches to be listed
                  immediately instead of ringing the bell.
           **show-all-if-unmodified (Off)**
                  This alters the default behavior of the completion
                  functions in a fashion similar to **show-all-if-ambiguous**.
                  If set to **On** , words which have more than one possible
                  completion without any possible partial completion (the
                  possible completions don't share a common prefix) cause the
                  matches to be listed immediately instead of ringing the
                  bell.
           **show-mode-in-prompt (Off)**
                  If set to **On** , add a string to the beginning of the prompt
                  indicating the editing mode: emacs, vi command, or vi
                  insertion.  The mode strings are user-settable (e.g.,
                  _emacs-mode-string_).
           **skip-completed-text (Off)**
                  If set to **On** , this alters the default completion behavior
                  when inserting a single match into the line.  It's only
                  active when performing completion in the middle of a word.
                  If enabled, **readline** does not insert characters from the
                  completion that match characters after point in the word
                  being completed, so portions of the word following the
                  cursor are not duplicated.
           **vi-cmd-mode-string ((cmd))**
                  If the _show-mode-in-prompt_ variable is enabled, this string
                  is displayed immediately before the last line of the
                  primary prompt when vi editing mode is active and in
                  command mode.  The value is expanded like a key binding, so
                  the standard set of meta- and control- prefixes and
                  backslash escape sequences is available.  The \1 and \2
                  escapes begin and end sequences of non-printing characters,
                  which can be used to embed a terminal control sequence into
                  the mode string.
           **vi-ins-mode-string ((ins))**
                  If the _show-mode-in-prompt_ variable is enabled, this string
                  is displayed immediately before the last line of the
                  primary prompt when vi editing mode is active and in
                  insertion mode.  The value is expanded like a key binding,
                  so the standard set of meta- and control- prefixes and
                  backslash escape sequences is available.  The \1 and \2
                  escapes begin and end sequences of non-printing characters,
                  which can be used to embed a terminal control sequence into
                  the mode string.
           **visible-stats (Off)**
                  If set to **On** , a character denoting a file's type as
                  reported by stat(2) is appended to the filename when
                  listing possible completions.
    
       **Readline Conditional Constructs**
           **Readline** implements a facility similar in spirit to the
           conditional compilation features of the C preprocessor which
           allows key bindings and variable settings to be performed as the
           result of tests.  There are four parser directives available.
    
           **$if** The **$if** construct allows bindings to be made based on the
                  editing mode, the terminal being used, or the application
                  using **readline**.  The text of the test, after any comparison
                  operator, extends to the end of the line; unless otherwise
                  noted, no characters are required to isolate it.
    
                  **mode** The **mode=** form of the **$if** directive is used to test
                         whether **readline** is in emacs or vi mode.  This may
                         be used in conjunction with the **set keymap** command,
                         for instance, to set bindings in the _emacs-standard_
                         and _emacs-ctlx_ keymaps only if **readline** is starting
                         out in emacs mode.
    
                  **term** The **term=** form may be used to include terminal-
                         specific key bindings, perhaps to bind the key
                         sequences output by the terminal's function keys.
                         The word on the right side of the **=** is tested
                         against both the full name of the terminal and the
                         portion of the terminal name before the first **-**.
                         This allows _xterm_ to match both _xterm_ and
                         _xterm-256color_ , for instance.
    
                  **version**
                         The **version** test may be used to perform comparisons
                         against specific **readline** versions.  The **version**
                         expands to the current **readline** version.  The set of
                         comparison operators includes **=** , (and **==**), **!=** , **< =**,
                         **> =**, **<** , and **>**.  The version number supplied on the
                         right side of the operator consists of a major
                         version number, an optional decimal point, and an
                         optional minor version (e.g., **7.1**).  If the minor
                         version is omitted, it defaults to **0**.  The operator
                         may be separated from the string **version** and from
                         the version number argument by whitespace.
    
                  _application_
                         The _application_ construct is used to include
                         application-specific settings.  Each program using
                         the **readline** library sets the _application name_ , and
                         an initialization file can test for a particular
                         value.  This could be used to bind key sequences to
                         functions useful for a specific program.  For
                         instance, the following command adds a key sequence
                         that quotes the current or previous word in **bash** :
    
                         **$if** Bash
                         # Quote the current or previous word
                         "\C-xq": "\eb\"\ef\""
                         **$endif**
    
                  _variable_
                         The _variable_ construct provides simple equality
                         tests for **readline** variables and values.  The
                         permitted comparison operators are _=_ , _==_ , and _!=_.
                         The variable name must be separated from the
                         comparison operator by whitespace; the operator may
                         be separated from the value on the right hand side
                         by whitespace.  String and boolean variables may be
                         tested.  Boolean variables must be tested against
                         the values _on_ and _off_.
    
           **$else** Commands in this branch of the **$if** directive are executed
                  if the test fails.
    
           **$endif** This command, as seen in the previous example, terminates
                  an **$if** command.
    
           **$include**
                  This directive takes a single filename as an argument and
                  reads commands and key bindings from that file.  For
                  example, the following directive would read _/etc/inputrc_ :
    
                  **$include** _/etc/inputrc_
    
       **Searching**
           **Readline** provides commands for searching through the command
           history (see **HISTORY** below) for lines containing a specified
           string.  There are two search modes: _incremental_ and _non-_
           _incremental_.
    
           Incremental searches begin before the user has finished typing the
           search string.  As each character of the search string is typed,
           **readline** displays the next entry from the history matching the
           string typed so far.  An incremental search requires only as many
           characters as needed to find the desired history entry.  When
           using emacs editing mode, type **C-r** to search backward in the
           history for a particular string.  Typing **C-s** searches forward
           through the history.  The characters present in the value of the
           **isearch-terminators** variable are used to terminate an incremental
           search.  If that variable has not been assigned a value, _ESC_ and
           **C-j** terminate an incremental search.  **C-g** aborts an incremental
           search and restores the original line.  When the search is
           terminated, the history entry containing the search string becomes
           the current line.
    
           To find other matching entries in the history list, type **C-r** or
           **C-s** as appropriate.  This searches backward or forward in the
           history for the next entry matching the search string typed so
           far.  Any other key sequence bound to a **readline** command
           terminates the search and executes that command.  For instance, a
           newline terminates the search and accepts the line, thereby
           executing the command from the history list.  A movement command
           will terminate the search, make the last line found the current
           line, and begin editing.
    
           **Readline** remembers the last incremental search string.  If two
           **C-r** s are typed without any intervening characters defining a new
           search string, **readline** uses any remembered search string.
    
           Non-incremental searches read the entire search string before
           starting to search for matching history entries.  The search
           string may be typed by the user or be part of the contents of the
           current line.
    
       **Readline Command Names**
           The following is a list of the names of the commands and the
           default key sequences to which they are bound.  Command names
           without an accompanying key sequence are unbound by default.
    
           In the following descriptions, _point_ refers to the current cursor
           position, and _mark_ refers to a cursor position saved by the
           **set-mark** command.  The text between the point and mark is referred
           to as the _region_.  **Readline** has the concept of an _active region_ :
           when the region is active, **readline** redisplay highlights the
           region using the value of the **active-region-start-color** variable.
           The **enable-active-region readline** variable turns this on and off.
           Several commands set the region to active; those are noted below.
    
       **Commands for Moving**
           **beginning-of-line (C-a)**
                  Move to the start of the current line.  This may also be
                  bound to the Home key on some keyboards.
           **end-of-line (C-e)**
                  Move to the end of the line.  This may also be bound to the
                  End key on some keyboards.
           **forward-char (C-f)**
                  Move forward a character.  This may also be bound to the
                  right arrow key on some keyboards.
           **backward-char (C-b)**
                  Move back a character.  This may also be bound to the left
                  arrow key on some keyboards.
           **forward-word (M-f)**
                  Move forward to the end of the next word.  Words are
                  composed of alphanumeric characters (letters and digits).
           **backward-word (M-b)**
                  Move back to the start of the current or previous word.
                  Words are composed of alphanumeric characters (letters and
                  digits).
           **shell-forward-word (M-C-f)**
                  Move forward to the end of the next word.  Words are
                  delimited by non-quoted shell metacharacters.
           **shell-backward-word (M-C-b)**
                  Move back to the start of the current or previous word.
                  Words are delimited by non-quoted shell metacharacters.
           **previous-screen-line**
                  Attempt to move point to the same physical screen column on
                  the previous physical screen line.  This will not have the
                  desired effect if the current **readline** line does not take
                  up more than one physical line or if point is not greater
                  than the length of the prompt plus the screen width.
           **next-screen-line**
                  Attempt to move point to the same physical screen column on
                  the next physical screen line.  This will not have the
                  desired effect if the current **readline** line does not take
                  up more than one physical line or if the length of the
                  current **readline** line is not greater than the length of the
                  prompt plus the screen width.
           **clear-display (M-C-l)**
                  Clear the screen and, if possible, the terminal's
                  scrollback buffer, then redraw the current line, leaving
                  the current line at the top of the screen.
           **clear-screen (C-l)**
                  Clear the screen, then redraw the current line, leaving the
                  current line at the top of the screen.  With a numeric
                  argument, refresh the current line without clearing the
                  screen.
           **redraw-current-line**
                  Refresh the current line.
    
       **Commands for Manipulating the History**
           **accept-line (Newline, Return)**
                  Accept the line regardless of where the cursor is.  If this
                  line is non-empty, add it to the history list according to
                  the state of the **HISTCONTROL** and **HISTIGNORE** variables.  If
                  the line is a modified history line, restore the history
                  line to its original state.
           **previous-history (C-p)**
                  Fetch the previous command from the history list, moving
                  back in the list.  This may also be bound to the up arrow
                  key on some keyboards.
           **next-history (C-n)**
                  Fetch the next command from the history list, moving
                  forward in the list.  This may also be bound to the down
                  arrow key on some keyboards.
           **beginning-of-history (M- <)**
                  Move to the first line in the history.
           **end-of-history (M- >)**
                  Move to the end of the input history, i.e., the line
                  currently being entered.
           **operate-and-get-next (C-o)**
                  Accept the current line for execution as if a newline had
                  been entered, and fetch the next line relative to the
                  current line from the history for editing.  A numeric
                  argument, if supplied, specifies the history entry to use
                  instead of the current line.
           **fetch-history**
                  With a numeric argument, fetch that entry from the history
                  list and make it the current line.  Without an argument,
                  move back to the first entry in the history list.
           **reverse-search-history (C-r)**
                  Search backward starting at the current line and moving
                  “up” through the history as necessary.  This is an
                  incremental search.  This command sets the region to the
                  matched text and activates the region.
           **forward-search-history (C-s)**
                  Search forward starting at the current line and moving
                  “down” through the history as necessary.  This is an
                  incremental search.  This command sets the region to the
                  matched text and activates the region.
           **non-incremental-reverse-search-history (M-p)**
                  Search backward through the history starting at the current
                  line using a non-incremental search for a string supplied
                  by the user.  The search string may match anywhere in a
                  history line.
           **non-incremental-forward-search-history (M-n)**
                  Search forward through the history using a non-incremental
                  search for a string supplied by the user.  The search
                  string may match anywhere in a history line.
           **history-search-backward**
                  Search backward through the history for the string of
                  characters between the start of the current line and the
                  point.  The search string must match at the beginning of a
                  history line.  This is a non-incremental search.  This may
                  be bound to the Page Up key on some keyboards.
           **history-search-forward**
                  Search forward through the history for the string of
                  characters between the start of the current line and the
                  point.  The search string must match at the beginning of a
                  history line.  This is a non-incremental search.  This may
                  be bound to the Page Down key on some keyboards.
           **history-substring-search-backward**
                  Search backward through the history for the string of
                  characters between the start of the current line and the
                  point.  The search string may match anywhere in a history
                  line.  This is a non-incremental search.
           **history-substring-search-forward**
                  Search forward through the history for the string of
                  characters between the start of the current line and the
                  point.  The search string may match anywhere in a history
                  line.  This is a non-incremental search.
           **yank-nth-arg (M-C-y)**
                  Insert the first argument to the previous command (usually
                  the second word on the previous line) at point.  With an
                  argument _n_ , insert the _n_ th word from the previous command
                  (the words in the previous command begin with word 0).  A
                  negative argument inserts the _n_ th word from the end of the
                  previous command.  Once the argument _n_ is computed, this
                  uses the history expansion facilities to extract the _n_ th
                  word, as if the “!_n_ ” history expansion had been specified.
           **yank-last-arg (M-., M-_)**
                  Insert the last argument to the previous command (the last
                  word of the previous history entry).  With a numeric
                  argument, behave exactly like **yank-nth-arg**.  Successive
                  calls to **yank-last-arg** move back through the history list,
                  inserting the last word (or the word specified by the
                  argument to the first call) of each line in turn.  Any
                  numeric argument supplied to these successive calls
                  determines the direction to move through the history.  A
                  negative argument switches the direction through the
                  history (back or forward).  This uses the history expansion
                  facilities to extract the last word, as if the “!$” history
                  expansion had been specified.
           **shell-expand-line (M-C-e)**
                  Expand the line by performing shell word expansions.  This
                  performs alias and history expansion, **$** '_string_ ' and
                  **$** "_string_ " quoting, tilde expansion, parameter and variable
                  expansion, arithmetic expansion, command and process
                  substitution, word splitting, and quote removal.  An
                  explicit argument suppresses command and process
                  substitution.  See **HISTORY EXPANSION** below for a
                  description of history expansion.
           **history-expand-line (M-^)**
                  Perform history expansion on the current line.  See **HISTORY**
                  **EXPANSION** below for a description of history expansion.
           **magic-space**
                  Perform history expansion on the current line and insert a
                  space.  See **HISTORY EXPANSION** below for a description of
                  history expansion.
           **alias-expand-line**
                  Perform alias expansion on the current line.  See **ALIASES**
                  above for a description of alias expansion.
           **history-and-alias-expand-line**
                  Perform history and alias expansion on the current line.
           **insert-last-argument (M-., M-_)**
                  A synonym for **yank-last-arg**.
           **edit-and-execute-command (C-x C-e)**
                  Invoke an editor on the current command line, and execute
                  the result as shell commands.  **Bash** attempts to invoke
                  **$VISUAL** , **$EDITOR** , and _emacs_ as the editor, in that order.
    
       **Commands for Changing Text**
           _end-of-file_ **(usually C-d)**
                  The character indicating end-of-file as set, for example,
                  by stty(1).  If this character is read when there are no
                  characters on the line, and point is at the beginning of
                  the line, **readline** interprets it as the end of input and
                  returns **EOF**.
           **delete-char (C-d)**
                  Delete the character at point.  If this function is bound
                  to the same character as the tty **EOF** character, as **C-d**
                  commonly is, see above for the effects.  This may also be
                  bound to the Delete key on some keyboards.
           **backward-delete-char (Rubout)**
                  Delete the character behind the cursor.  When given a
                  numeric argument, save the deleted text on the kill ring.
           **forward-backward-delete-char**
                  Delete the character under the cursor, unless the cursor is
                  at the end of the line, in which case the character behind
                  the cursor is deleted.
           **quoted-insert (C-q, C-v)**
                  Add the next character typed to the line verbatim.  This is
                  how to insert characters like **C-q** , for example.
           **tab-insert (C-v TAB)**
                  Insert a tab character.
           **self-insert (a, b, A, 1, !,**...**)**
                  Insert the character typed.
           **bracketed-paste-begin**
                  This function is intended to be bound to the “bracketed
                  paste” escape sequence sent by some terminals, and such a
                  binding is assigned by default.  It allows **readline** to
                  insert the pasted text as a single unit without treating
                  each character as if it had been read from the keyboard.
                  The pasted characters are inserted as if each one was bound
                  to **self-insert** instead of executing any editing commands.
                  Bracketed paste sets the region to the inserted text and
                  activates the region.
           **transpose-chars (C-t)**
                  Drag the character before point forward over the character
                  at point, moving point forward as well.  If point is at the
                  end of the line, then this transposes the two characters
                  before point.  Negative arguments have no effect.
           **transpose-words (M-t)**
                  Drag the word before point past the word after point,
                  moving point past that word as well.  If point is at the
                  end of the line, this transposes the last two words on the
                  line.
           **shell-transpose-words (M-C-t)**
                  Drag the word before point past the word after point,
                  moving point past that word as well.  If the insertion
                  point is at the end of the line, this transposes the last
                  two words on the line.  Word boundaries are the same as
                  **shell-forward-word** and **shell-backward-word**.
           **upcase-word (M-u)**
                  Uppercase the current (or following) word.  With a negative
                  argument, uppercase the previous word, but do not move
                  point.
           **downcase-word (M-l)**
                  Lowercase the current (or following) word.  With a negative
                  argument, lowercase the previous word, but do not move
                  point.
           **capitalize-word (M-c)**
                  Capitalize the current (or following) word.  With a
                  negative argument, capitalize the previous word, but do not
                  move point.
           **overwrite-mode**
                  Toggle overwrite mode.  With an explicit positive numeric
                  argument, switches to overwrite mode.  With an explicit
                  non-positive numeric argument, switches to insert mode.
                  This command affects only **emacs** mode; **vi** mode does
                  overwrite differently.  Each call to _readline()_ starts in
                  insert mode.
                  In overwrite mode, characters bound to **self-insert** replace
                  the text at point rather than pushing the text to the
                  right.  Characters bound to **backward-delete-char** replace
                  the character before point with a space.  By default, this
                  command is unbound, but may be bound to the Insert key on
                  some keyboards.
    
       **Killing and Yanking**
           **kill-line (C-k)**
                  Kill the text from point to the end of the current line.
                  With a negative numeric argument, kill backward from the
                  cursor to the beginning of the line.
           **backward-kill-line (C-x Rubout)**
                  Kill backward to the beginning of the current line.  With a
                  negative numeric argument, kill forward from the cursor to
                  the end of the line.
           **unix-line-discard (C-u)**
                  Kill backward from point to the beginning of the line,
                  saving the killed text on the kill-ring.
           **kill-whole-line**
                  Kill all characters on the current line, no matter where
                  point is.
           **kill-word (M-d)**
                  Kill from point to the end of the current word, or if
                  between words, to the end of the next word.  Word
                  boundaries are the same as those used by **forward-word**.
           **backward-kill-word (M-Rubout)**
                  Kill the word behind point.  Word boundaries are the same
                  as those used by **backward-word**.
           **shell-kill-word (M-C-d)**
                  Kill from point to the end of the current word, or if
                  between words, to the end of the next word.  Word
                  boundaries are the same as those used by
                  **shell-forward-word**.
           **shell-backward-kill-word**
                  Kill the word behind point.  Word boundaries are the same
                  as those used by **shell-backward-word**.
           **unix-word-rubout (C-w)**
                  Kill the word behind point, using white space as a word
                  boundary, saving the killed text on the kill-ring.
           **unix-filename-rubout**
                  Kill the word behind point, using white space and the slash
                  character as the word boundaries, saving the killed text on
                  the kill-ring.
           **delete-horizontal-space (M-\)**
                  Delete all spaces and tabs around point.
           **kill-region**
                  Kill the text in the current region.
           **copy-region-as-kill**
                  Copy the text in the region to the kill buffer, so it can
                  be yanked immediately.
           **copy-backward-word**
                  Copy the word before point to the kill buffer.  The word
                  boundaries are the same as **backward-word**.
           **copy-forward-word**
                  Copy the word following point to the kill buffer.  The word
                  boundaries are the same as **forward-word**.
           **yank (C-y)**
                  Yank the top of the kill ring into the buffer at point.
           **yank-pop (M-y)**
                  Rotate the kill ring, and yank the new top.  Only works
                  following **yank** or **yank-pop**.
    
       **Numeric Arguments**
           **digit-argument (M-0, M-1,**...**, M--)**
                  Add this digit to the argument already accumulating, or
                  start a new argument.  M-- starts a negative argument.
           **universal-argument**
                  This is another way to specify an argument.  If this
                  command is followed by one or more digits, optionally with
                  a leading minus sign, those digits define the argument.  If
                  the command is followed by digits, executing
                  **universal-argument** again ends the numeric argument, but is
                  otherwise ignored.  As a special case, if this command is
                  immediately followed by a character that is neither a digit
                  nor minus sign, the argument count for the next command is
                  multiplied by four.  The argument count is initially one,
                  so executing this function the first time makes the
                  argument count four, a second time makes the argument count
                  sixteen, and so on.
    
       **Completing**
           **complete (TAB)**
                  Attempt to perform completion on the text before point.
                  **Bash** attempts completion by first checking for any
                  programmable completions for the command word (see
                  **Programmable Completion** below), otherwise treating the text
                  as a variable (if the text begins with **$**), username (if the
                  text begins with **~**), hostname (if the text begins with **@**),
                  or command (including aliases, functions, and builtins) in
                  turn.  If none of these produces a match, it falls back to
                  filename completion.
           **possible-completions (M-?)**
                  List the possible completions of the text before point.
                  When displaying completions, **readline** sets the number of
                  columns used for display to the value of **completion-**
                  **display-width** , the value of the shell variable **COLUMNS** , or
                  the screen width, in that order.
           **insert-completions (M-*)**
                  Insert all completions of the text before point that would
                  have been generated by **possible-completions** , separated by a
                  space.
           **menu-complete**
                  Similar to **complete** , but replaces the word to be completed
                  with a single match from the list of possible completions.
                  Repeatedly executing **menu-complete** steps through the list
                  of possible completions, inserting each match in turn.  At
                  the end of the list of completions, **menu-complete** rings the
                  bell (subject to the setting of **bell-style**) and restores
                  the original text.  An argument of _n_ moves _n_ positions
                  forward in the list of matches; a negative argument moves
                  backward through the list.  This command is intended to be
                  bound to **TAB** , but is unbound by default.
           **menu-complete-backward**
                  Identical to **menu-complete** , but moves backward through the
                  list of possible completions, as if **menu-complete** had been
                  given a negative argument.  This command is unbound by
                  default.
           **export-completions**
                  Perform completion on the word before point as described
                  above and write the list of possible completions to
                  **readline** 's output stream using the following format,
                  writing information on separate lines:
    
                  •      the number of matches _N_ ;
                  •      the word being completed;
                  •      _S_ :_E_ , where _S_ and _E_ are the start and end offsets of
                         the word in the **readline** line buffer; then
                  •      each match, one per line
    
                  If there are no matches, the first line will be “0”, and
                  this command does not print any output after the _S_ :_E_.  If
                  there is only a single match, this prints a single line
                  containing it.  If there is more than one match, this
                  prints the common prefix of the matches, which may be
                  empty, on the first line after the _S_ :_E_ , then the matches on
                  subsequent lines.  In this case, _N_ will include the first
                  line with the common prefix.
    
                  The user or application should be able to accommodate the
                  possibility of a blank line.  The intent is that the user
                  or application reads _N_ lines after the line containing _S_ :_E_
                  to obtain the match list.  This command is unbound by
                  default.
    
           **delete-char-or-list**
                  Deletes the character under the cursor if not at the
                  beginning or end of the line (like **delete-char**).  At the
                  end of the line, it behaves identically to
                  **possible-completions**.  This command is unbound by default.
    
           **complete-filename (M-/)**
                  Attempt filename completion on the text before point.
    
           **possible-filename-completions (C-x /)**
                  List the possible completions of the text before point,
                  treating it as a filename.
    
           **complete-username (M-~)**
                  Attempt completion on the text before point, treating it as
                  a username.
    
           **possible-username-completions (C-x ~)**
                  List the possible completions of the text before point,
                  treating it as a username.
    
           **complete-variable (M-$)**
                  Attempt completion on the text before point, treating it as
                  a shell variable.
    
           **possible-variable-completions (C-x $)**
                  List the possible completions of the text before point,
                  treating it as a shell variable.
    
           **complete-hostname (M-@)**
                  Attempt completion on the text before point, treating it as
                  a hostname.
    
           **possible-hostname-completions (C-x @)**
                  List the possible completions of the text before point,
                  treating it as a hostname.
    
           **complete-command (M-!)**
                  Attempt completion on the text before point, treating it as
                  a command name.  Command completion attempts to match the
                  text against aliases, reserved words, shell functions,
                  shell builtins, and finally executable filenames, in that
                  order.
    
           **possible-command-completions (C-x !)**
                  List the possible completions of the text before point,
                  treating it as a command name.
    
           **dynamic-complete-history (M-TAB)**
                  Attempt completion on the text before point, comparing the
                  text against history list entries for possible completion
                  matches.
    
           **dabbrev-expand**
                  Attempt menu completion on the text before point, comparing
                  the text against lines from the history list for possible
                  completion matches.
    
           **complete-into-braces (M-{)**
                  Perform filename completion and insert the list of possible
                  completions enclosed within braces so the list is available
                  to the shell (see **Brace Expansion** above).
    
       **Keyboard Macros**
           **start-kbd-macro (C-x ()**
                  Begin saving the characters typed into the current keyboard
                  macro.
           **end-kbd-macro (C-x ))**
                  Stop saving the characters typed into the current keyboard
                  macro and store the definition.
           **call-last-kbd-macro (C-x e)**
                  Re-execute the last keyboard macro defined, by making the
                  characters in the macro appear as if typed at the keyboard.
           **print-last-kbd-macro ()**
                  Print the last keyboard macro defined in a format suitable
                  for the _inputrc_ file.
    
       **Miscellaneous**
           **re-read-init-file (C-x C-r)**
                  Read in the contents of the _inputrc_ file, and incorporate
                  any bindings or variable assignments found there.
           **abort (C-g)**
                  Abort the current editing command and ring the terminal's
                  bell (subject to the setting of **bell-style**).
           **do-lowercase-version (M-A, M-B, M-**_x_**,**...**)**
                  If the metafied character _x_ is uppercase, run the command
                  that is bound to the corresponding metafied lowercase
                  character.  The behavior is undefined if _x_ is already
                  lowercase.
           **prefix-meta (ESC)**
                  Metafy the next character typed.  **ESC f** is equivalent to
                  **Meta-f**.
           **undo (C-_, C-x C-u)**
                  Incremental undo, separately remembered for each line.
           **revert-line (M-r)**
                  Undo all changes made to this line.  This is like executing
                  the **undo** command enough times to return the line to its
                  initial state.
           **tilde-expand (M- &)**
                  Perform tilde expansion on the current word.
           **set-mark (C-@, M- <space>)**
                  Set the mark to the point.  If a numeric argument is
                  supplied, set the mark to that position.
           **exchange-point-and-mark (C-x C-x)**
                  Swap the point with the mark.  Set the current cursor
                  position to the saved position, then set the mark to the
                  old cursor position.
           **character-search (C-])**
                  Read a character and move point to the next occurrence of
                  that character.  A negative argument searches for previous
                  occurrences.
           **character-search-backward (M-C-])**
                  Read a character and move point to the previous occurrence
                  of that character.  A negative argument searches for
                  subsequent occurrences.
           **skip-csi-sequence**
                  Read enough characters to consume a multi-key sequence such
                  as those defined for keys like Home and End.  CSI sequences
                  begin with a Control Sequence Indicator (CSI), usually _ESC_
                  _[_.  If this sequence is bound to “\e[”, keys producing CSI
                  sequences have no effect unless explicitly bound to a
                  **readline** command, instead of inserting stray characters
                  into the editing buffer.  This is unbound by default, but
                  usually bound to _ESC [_.
           **insert-comment (M-#)**
                  Without a numeric argument, insert the value of the
                  **readline comment-begin** variable at the beginning of the
                  current line.  If a numeric argument is supplied, this
                  command acts as a toggle: if the characters at the
                  beginning of the line do not match the value of
                  **comment-begin** , insert the value; otherwise delete the
                  characters in **comment-begin** from the beginning of the line.
                  In either case, the line is accepted as if a newline had
                  been typed.  The default value of **comment-begin** causes this
                  command to make the current line a shell comment.  If a
                  numeric argument causes the comment character to be
                  removed, the line will be executed by the shell.
           **spell-correct-word (C-x s)**
                  Perform spelling correction on the current word, treating
                  it as a directory or filename, in the same way as the
                  **cdspell** shell option.  Word boundaries are the same as
                  those used by **shell-forward-word**.
           **glob-complete-word (M-g)**
                  Treat the word before point as a pattern for pathname
                  expansion, with an asterisk implicitly appended, then use
                  the pattern to generate a list of matching file names for
                  possible completions.
           **glob-expand-word (C-x *)**
                  Treat the word before point as a pattern for pathname
                  expansion, and insert the list of matching file names,
                  replacing the word.  If a numeric argument is supplied,
                  append a ***** before pathname expansion.
           **glob-list-expansions (C-x g)**
                  Display the list of expansions that would have been
                  generated by **glob-expand-word** and redisplay the line.  If a
                  numeric argument is supplied, append a ***** before pathname
                  expansion.
           **dump-functions**
                  Print all of the functions and their key bindings to the
                  **readline** output stream.  If a numeric argument is supplied,
                  the output is formatted in such a way that it can be made
                  part of an _inputrc_ file.
           **dump-variables**
                  Print all of the settable **readline** variables and their
                  values to the **readline** output stream.  If a numeric
                  argument is supplied, the output is formatted in such a way
                  that it can be made part of an _inputrc_ file.
           **dump-macros**
                  Print all of the **readline** key sequences bound to macros and
                  the strings they output to the **readline** output stream.  If
                  a numeric argument is supplied, the output is formatted in
                  such a way that it can be made part of an _inputrc_ file.
           **execute-named-command (M-x)**
                  Read a bindable **readline** command name from the input and
                  execute the function to which it's bound, as if the key
                  sequence to which it was bound appeared in the input.  If
                  this function is supplied with a numeric argument, it
                  passes that argument to the function it executes.
           **display-shell-version (C-x C-v)**
                  Display version information about the current instance of
                  **bash**.
    
       **Programmable Completion**
           When a user attempts word completion for a command or an argument
           to a command for which a completion specification (a _compspec_) has
           been defined using the **complete** builtin (see **SHELL BUILTIN**
           **COMMANDS** below), **readline** invokes the programmable completion
           facilities.
    
           First, **bash** identifies the command name.  If a compspec has been
           defined for that command, the compspec is used to generate the
           list of possible completions for the word.  If the command word is
           the empty string (completion attempted at the beginning of an
           empty line), **bash** uses any compspec defined with the **-E** option to
           **complete**.  The **-I** option to **complete** indicates that the command
           word is the first non-assignment word on the line, or after a
           command delimiter such as **;** or **|**.  This usually indicates command
           name completion.
    
           If the command word is a full pathname, **bash** searches for a
           compspec for the full pathname first.  If there is no compspec for
           the full pathname, **bash** attempts to find a compspec for the
           portion following the final slash.  If those searches do not
           result in a compspec, or if there is no compspec for the command
           word, **bash** uses any compspec defined with the **-D** option to
           **complete** as the default.  If there is no default compspec, **bash**
           performs alias expansion on the command word as a final resort,
           and attempts to find a compspec for the command word resulting
           from any successful expansion.
    
           If a compspec is not found, **bash** performs its default completion
           as described above under **Completing**.  Otherwise, once a compspec
           has been found, **bash** uses it to generate the list of matching
           words.
    
           First, **bash** performs the _actions_ specified by the compspec.  This
           only returns matches which are prefixes of the word being
           completed.  When the **-f** or **-d** option is used for filename or
           directory name completion, **bash** uses the shell variable **FIGNORE** to
           filter the matches.
    
           Next, programmable completion generates matches specified by a
           pathname expansion pattern supplied as an argument to the **-G**
           option.  The words generated by the pattern need not match the
           word being completed.  **Bash** uses the **FIGNORE** variable to filter
           the matches, but does not use the **GLOBIGNORE** shell variable.
    
           Next, completion considers the string specified as the argument to
           the **-W** option.  The string is first split using the characters in
           the **IFS** special variable as delimiters.  This honors shell quoting
           within the string, in order to provide a mechanism for the words
           to contain shell metacharacters or characters in the value of **IFS**.
           Each word is then expanded using brace expansion, tilde expansion,
           parameter and variable expansion, command substitution, and
           arithmetic expansion, as described above under **EXPANSION**.  The
           results are split using the rules described above under **Word**
           **Splitting**.  The results of the expansion are prefix-matched
           against the word being completed, and the matching words become
           possible completions.
    
           After these matches have been generated, **bash** executes any shell
           function or command specified with the **-F** and **-C** options.  When
           the command or function is invoked, **bash** assigns values to the
           **COMP_LINE** , **COMP_POINT** , **COMP_KEY** , and **COMP_TYPE** variables as
           described above under **Shell Variables**.  If a shell function is
           being invoked, **bash** also sets the **COMP_WORDS** and **COMP_CWORD**
           variables.  When the function or command is invoked, the first
           argument (**$1**) is the name of the command whose arguments are being
           completed, the second argument (**$2**) is the word being completed,
           and the third argument (**$3**) is the word preceding the word being
           completed on the current command line.  There is no filtering of
           the generated completions against the word being completed; the
           function or command has complete freedom in generating the matches
           and they do not need to match a prefix of the word.
    
           Any function specified with **-F** is invoked first.  The function may
           use any of the shell facilities, including the **compgen** and **compopt**
           builtins described below, to generate the matches.  It must put
           the possible completions in the **COMPREPLY** array variable, one per
           array element.
    
           Next, any command specified with the **-C** option is invoked in an
           environment equivalent to command substitution.  It should print a
           list of completions, one per line, to the standard output.
           Backslash will escape a newline, if necessary.  These are added to
           the set of possible completions.
    
           After generating all of the possible completions, **bash** applies any
           filter specified with the **-X** option to the completions in the
           list.  The filter is a pattern as used for pathname expansion; a **&**
           in the pattern is replaced with the text of the word being
           completed.  A literal **& **may be escaped with a backslash; the
           backslash is removed before attempting a match.  Any completion
           that matches the pattern is removed from the list.  A leading **!**
           negates the pattern; in this case **bash** removes any completion that
           does not match the pattern.  If the **nocasematch** shell option is
           enabled, **bash** performs the match without regard to the case of
           alphabetic characters.
    
           Finally, programmable completion adds any prefix and suffix
           specified with the **-P** and **-S** options, respectively, to each
           completion, and returns the result to **readline** as the list of
           possible completions.
    
           If the previously-applied actions do not generate any matches, and
           the **-o dirnames** option was supplied to **complete** when the compspec
           was defined, **bash** attempts directory name completion.
    
           If the **-o plusdirs** option was supplied to **complete** when the
           compspec was defined, **bash** attempts directory name completion and
           adds any matches to the set of possible completions.
    
           By default, if a compspec is found, whatever it generates is
           returned to the completion code as the full set of possible
           completions.  The default **bash** completions and the **readline**
           default of filename completion are disabled.  If the **-o**
           **bashdefault** option was supplied to **complete** when the compspec was
           defined, and the compspec generates no matches, **bash** attempts its
           default completions.  If the compspec and, if attempted, the
           default **bash** completions generate no matches, and the **-o default**
           option was supplied to **complete** when the compspec was defined,
           programmable completion performs **readline** 's default completion.
    
           The options supplied to **complete** and **compopt** can control how
           **readline** treats the completions.  For instance, the _-o fullquote_
           option tells **readline** to quote the matches as if they were
           filenames.  See the description of **complete** below for details.
    
           When a compspec indicates that it wants directory name completion,
           the programmable completion functions force **readline** to append a
           slash to completed names which are symbolic links to directories,
           subject to the value of the **mark-directories readline** variable,
           regardless of the setting of the **mark-symlinked-directories**
           **readline** variable.
    
           There is some support for dynamically modifying completions.  This
           is most useful when used in combination with a default completion
           specified with **complete -D**.  It's possible for shell functions
           executed as completion functions to indicate that completion
           should be retried by returning an exit status of 124.  If a shell
           function returns 124, and changes the compspec associated with the
           command on which completion is being attempted (supplied as the
           first argument when the function is executed), programmable
           completion restarts from the beginning, with an attempt to find a
           new compspec for that command.  This can be used to build a set of
           completions dynamically as completion is attempted, rather than
           loading them all at once.
    
           For instance, assuming that there is a library of compspecs, each
           kept in a file corresponding to the name of the command, the
           following default completion function would load completions
           dynamically:
                  _completion_loader()
                  {
                    . "/etc/bash_completion.d/$1.sh" \
                      >/dev/null 2>&1 && return 124
                  }
                  complete -D -F _completion_loader \
                      -o bashdefault -o default
    


## SHELL BUILTIN COMMANDS



           Unless otherwise noted, each builtin command documented in this
           section as accepting options preceded by **-** accepts **--** to signify
           the end of the options.  The **:** , **true** , **false** , and **test** /**[** builtins
           do not accept options and do not treat **--** specially.  The **exit** ,
           **logout** , **return** , **break** , **continue** , **let** , and **shift** builtins accept
           and process arguments beginning with **-** without requiring **--**.
           Other builtins that accept arguments but are not specified as
           accepting options interpret arguments beginning with **-** as invalid
           options and require **--** to prevent this interpretation.
    
           **:**[_arguments_]
                  No effect; the command does nothing beyond expanding
                  _arguments_ and performing any specified redirections.  The
                  return status is zero.
    
           **.**[**-p** _path_] _filename_ [_arguments_]
           **source**[**-p** _path_] _filename_ [_arguments_]
                  The **.** command (**source**) reads and execute commands from
                  _filename_ in the current shell environment and returns the
                  exit status of the last command executed from _filename_.
    
                  If _filename_ does not contain a slash, **.** searches for it.
                  If the **-p** option is supplied, **.** treats _path_ as a colon-
                  separated list of directories in which to find _filename_ ;
                  otherwise, **.** uses the entries in **PATH** to find the directory
                  containing _filename_.  _filename_ does not need to be
                  executable.  When **bash** is not in posix mode, it searches
                  the current directory if _filename_ is not found in **PATH** , but
                  does not search the current directory if **-p** is supplied.
                  If the **sourcepath** option to the **shopt** builtin command is
                  turned off, **.** does not search **PATH**.
    
                  If any _arguments_ are supplied, they become the positional
                  parameters when _filename_ is executed.  Otherwise the
                  positional parameters are unchanged.
    
                  If the **-T** option is enabled, **.** inherits any trap on **DEBUG** ;
                  if it is not, any **DEBUG** trap string is saved and restored
                  around the call to **.** , and **.** unsets the **DEBUG** trap while it
                  executes.  If **-T** is not set, and the sourced file changes
                  the **DEBUG** trap, the new value persists after **.** completes.
                  The return status is the status of the last command
                  executed from _filename_ (0 if no commands are executed), and
                  non-zero if _filename_ is not found or cannot be read.
    
           **alias**[**-p**] [_name_[=_value_] ...]
                  With no arguments or with the **-p** option, **alias** prints the
                  list of aliases in the form **alias** _name_ =_value_ on standard
                  output.  When arguments are supplied, define an alias for
                  each _name_ whose _value_ is given.  A trailing space in _value_
                  causes the next word to be checked for alias substitution
                  when the alias is expanded during command parsing.  For
                  each _name_ in the argument list for which no _value_ is
                  supplied, print the name and value of the alias _name_.
                  **alias** returns true unless a _name_ is given (without a
                  corresponding =_value_) for which no alias has been defined.
    
           **bg**[_jobspec_ ...]
                  Resume each suspended job _jobspec_ in the background, as if
                  it had been started with **&**.  If _jobspec_ is not present, the
                  shell uses its notion of the _current job_.  **bg** _jobspec_
                  returns 0 unless run when job control is disabled or, when
                  run with job control enabled, any specified _jobspec_ was not
                  found or was started without job control.
    
           **bind**[**-m** _keymap_] [**-lsvSVX**]
           **bind**[**-m** _keymap_] [**-q** _function_] [**-u** _function_] [**-r** _keyseq_]
           **bind**[**-m** _keymap_] **-f** _filename_
           **bind**[**-m** _keymap_] **-x** _keyseq_[:] _shell-command_
           **bind**[**-m** _keymap_] _keyseq_ :_function-name_
           **bind**[**-m** _keymap_] **-p** |**-P**[_readline-command_]
           **bind**[**-m** _keymap_] _keyseq_ :_readline-command_
           **bind** _readline-command-line_
                  Display current **readline** key and function bindings, bind a
                  key sequence to a **readline** function or macro or to a shell
                  command, or set a **readline** variable.  Each non-option
                  argument is a key binding or command as it would appear in
                  a **readline** initialization file such as _.inputrc_ , but each
                  binding or command must be passed as a separate argument;
                  e.g., '"\C-x\C-r": re-read-init-file'.  In the following
                  descriptions, output available to be re-read is formatted
                  as commands that would appear in a **readline** initialization
                  file or that would be supplied as individual arguments to a
                  **bind** command.  Options, if supplied, have the following
                  meanings:
                  **-m** _keymap_
                         Use _keymap_ as the keymap to be affected by the
                         subsequent bindings.  Acceptable _keymap_ names are
                         _emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,_
                         _vi-move, vi-command_ , and _vi-insert_.  _vi_ is
                         equivalent to _vi-command_ (_vi-move_ is also a
                         synonym); _emacs_ is equivalent to _emacs-standard_.
                  **-l** List the names of all **readline** functions.
                  **-p** Display **readline** function names and bindings in such
                         a way that they can be used as an argument to a
                         subsequent **bind** command or in a **readline**
                         initialization file.  If arguments remain after
                         option processing, **bind** treats them as **readline**
                         command names and restricts output to those names.
                  **-P** List current **readline** function names and bindings.
                         If arguments remain after option processing, **bind**
                         treats them as **readline** command names and restricts
                         output to those names.
                  **-s** Display **readline** key sequences bound to macros and
                         the strings they output in such a way that they can
                         be used as an argument to a subsequent **bind** command
                         or in a **readline** initialization file.
                  **-S** Display **readline** key sequences bound to macros and
                         the strings they output.
                  **-v** Display **readline** variable names and values in such a
                         way that they can be used as an argument to a
                         subsequent **bind** command or in a **readline**
                         initialization file.
                  **-V** List current **readline** variable names and values.
                  **-f** _filename_
                         Read key bindings from _filename_.
                  **-q** _function_
                         Display key sequences that invoke the named **readline**
                         _function_.
                  **-u** _function_
                         Unbind all key sequences bound to the named **readline**
                         _function_.
                  **-r** _keyseq_
                         Remove any current binding for _keyseq_.
                  **-x** _keyseq_**[: ]**_shell-command_
                         Cause _shell-command_ to be executed whenever _keyseq_
                         is entered.  The separator between _keyseq_ and
                         _shell-command_ is either whitespace or a colon
                         optionally followed by whitespace.  If the separator
                         is whitespace, _shell-command_ must be enclosed in
                         double quotes and **readline** expands any of its
                         special backslash-escapes in _shell-command_ before
                         saving it.  If the separator is a colon, any
                         enclosing double quotes are optional, and **readline**
                         does not expand the command string before saving it.
                         Since the entire key binding expression must be a
                         single argument, it should be enclosed in single
                         quotes.  When _shell-command_ is executed, the shell
                         sets the **READLINE_LINE** variable to the contents of
                         the **readline** line buffer and the **READLINE_POINT** and
                         **READLINE_MARK** variables to the current location of
                         the insertion point and the saved insertion point
                         (the mark), respectively.  The shell assigns any
                         numeric argument the user supplied to the
                         **READLINE_ARGUMENT** variable.  If there was no
                         argument, that variable is not set.  If the executed
                         command changes the value of any of **READLINE_LINE** ,
                         **READLINE_POINT** , or **READLINE_MARK** , those new values
                         will be reflected in the editing state.
                  **-X** List all key sequences bound to shell commands and
                         the associated commands in a format that can be
                         reused as an argument to a subsequent **bind** command.
    
                  The return value is 0 unless an unrecognized option is
                  supplied or an error occurred.
    
           **break**[_n_]
                  Exit from within a **for** , **while** , **until** , or **select** loop.  If _n_
                  is specified, **break** exits _n_ enclosing loops.  _n_ must be ≥
                  1.  If _n_ is greater than the number of enclosing loops, all
                  enclosing loops are exited.  The return value is 0 unless _n_
                  is not greater than or equal to 1.
    
           **builtin** _shell-builtin_ [_arguments_]
                  Execute the specified shell builtin _shell-builtin_ , passing
                  it _arguments_ , and return its exit status.  This is useful
                  when defining a function whose name is the same as a shell
                  builtin, retaining the functionality of the builtin within
                  the function.  The **cd** builtin is commonly redefined this
                  way.  The return status is false if _shell-builtin_ is not a
                  shell builtin command.
    
           **caller**[_expr_]
                  Returns the context of any active subroutine call (a shell
                  function or a script executed with the **.** or **source**
                  builtins).
    
                  Without _expr_ , **caller** displays the line number and source
                  filename of the current subroutine call.  If a non-negative
                  integer is supplied as _expr_ , **caller** displays the line
                  number, subroutine name, and source file corresponding to
                  that position in the current execution call stack.  This
                  extra information may be used, for example, to print a
                  stack trace.  The current frame is frame 0.
    
                  The return value is 0 unless the shell is not executing a
                  subroutine call or _expr_ does not correspond to a valid
                  position in the call stack.
    
           **cd**[**-L**] [**-@**] [_dir_]
           **cd -P**[**-e**] [**-@**] [_dir_]
                  Change the current directory to _dir_.  if _dir_ is not
                  supplied, the value of the **HOME** shell variable is used as
                  _dir_.  The variable **CDPATH** exists, and _dir_ does not begin
                  with a slash (/), **cd** uses it as a search path: the shell
                  searches each directory name in **CDPATH** for _dir_.
                  Alternative directory names in **CDPATH** are separated by a
                  colon (:).  A null directory name in **CDPATH** is the same as
                  the current directory, i.e., “.”.
    
                  The **-P** option causes **cd** to use the physical directory
                  structure by resolving symbolic links while traversing _dir_
                  and before processing instances of _.._ in _dir_ (see also the
                  **-P** option to the **set** builtin command).
    
                  The **-L** option forces **cd** to follow symbolic links by
                  resolving the link after processing instances of _.._ in _dir_.
                  If _.._ appears in _dir_ , **cd** processes it by removing the
                  immediately previous pathname component from _dir_ , back to a
                  slash or the beginning of _dir_ , and verifying that the
                  portion of _dir_ it has processed to that point is still a
                  valid directory name after removing the pathname component.
                  If it is not a valid directory name, **cd** returns a non-zero
                  status.  If neither **-L** nor **-P** is supplied, **cd** behaves as if
                  **-L** had been supplied.
    
                  If the **-e** option is supplied with **-P** , and **cd** cannot
                  successfully determine the current working directory after
                  a successful directory change, it returns a non-zero
                  status.
    
                  On systems that support it, the **-@** option presents the
                  extended attributes associated with a file as a directory.
    
                  An argument of **-** is converted to **$OLDPWD** before attempting
                  the directory change.
    
                  If **cd** uses a non-empty directory name from **CDPATH** , or if **-**
                  is the first argument, and the directory change is
                  successful, **cd** writes the absolute pathname of the new
                  working directory to the standard output.
    
                  If the directory change is successful, **cd** sets the value of
                  the **PWD** environment variable to the new directory name, and
                  sets the **OLDPWD** environment variable to the value of the
                  current working directory before the change.
    
                  The return value is true if the directory was successfully
                  changed; false otherwise.
    
           **command**[**-pVv**] _command_ [_arg_ ...]
                  The **command** builtin runs _command_ with _args_ suppressing the
                  normal shell function lookup for _command_.  Only builtin
                  commands or commands found in the **PATH** named _command_ are
                  executed.  If the **-p** option is supplied, the search for
                  _command_ is performed using a default value for **PATH** that is
                  guaranteed to find all of the standard utilities.
    
                  If either the **-V** or **-v** option is supplied, **command** prints a
                  description of _command_.  The **-v** option displays a single
                  word indicating the command or filename used to invoke
                  _command_ ; the **-V** option produces a more verbose description.
    
                  If the **-V** or **-v** option is supplied, the exit status is zero
                  if _command_ was found, and non-zero if not.  If neither
                  option is supplied and an error occurred or _command_ cannot
                  be found, the exit status is 127.  Otherwise, the exit
                  status of the **command** builtin is the exit status of
                  _command_.
    
           **compgen**[**-V** _varname_] [_option_] [_word_]
                  Generate possible completion matches for _word_ according to
                  the _option_ s, which may be any option accepted by the
                  **complete** builtin with the exceptions of **-p** , **-r** , **-D** , **-E** , and
                  **-I** , and write the matches to the standard output.
    
                  If the **-V** option is supplied, **compgen** stores the generated
                  completions into the indexed array variable _varname_ instead
                  of writing them to the standard output.
    
                  When using the **-F** or **-C** options, the various shell
                  variables set by the programmable completion facilities,
                  while available, will not have useful values.
    
                  The matches will be generated in the same way as if the
                  programmable completion code had generated them directly
                  from a completion specification with the same flags.  If
                  _word_ is specified, only those completions matching _word_
                  will be displayed or stored.
    
                  The return value is true unless an invalid option is
                  supplied, or no matches were generated.
    
           **complete**[**-abcdefgjksuv**] [**-o** _comp-option_] [**-DEI**] [**-A** _action_]
                  [**-G** _globpat_] [**-W** _wordlist_] [**-F** _function_] [**-C** _command_]
                  [**-X** _filterpat_] [**-P** _prefix_] [**-S** _suffix_] _name_ [_name_ ...]
           **complete -pr**[**-DEI**] [_name_ ...]
                  Specify how arguments to each _name_ should be completed.
    
                  If the **-p** option is supplied, or if no options or _name_ s are
                  supplied, print existing completion specifications in a way
                  that allows them to be reused as input.  The **-r** option
                  removes a completion specification for each _name_ , or, if no
                  _name_ s are supplied, all completion specifications.
    
                  The **-D** option indicates that other supplied options and
                  actions should apply to the “default” command completion;
                  that is, completion attempted on a command for which no
                  completion has previously been defined.  The **-E** option
                  indicates that other supplied options and actions should
                  apply to “empty” command completion; that is, completion
                  attempted on a blank line.  The **-I** option indicates that
                  other supplied options and actions should apply to
                  completion on the initial non-assignment word on the line,
                  or after a command delimiter such as **;** or **|** , which is
                  usually command name completion.  If multiple options are
                  supplied, the **-D** option takes precedence over **-E** , and both
                  take precedence over **-I**.  If any of **-D** , **-E** , or **-I** are
                  supplied, any other _name_ arguments are ignored; these
                  completions only apply to the case specified by the option.
    
                  The process of applying these completion specifications
                  when attempting word completion  is described above under
                  **Programmable Completion**.
    
                  Other options, if specified, have the following meanings.
                  The arguments to the **-G** , **-W** , and **-X** options (and, if
                  necessary, the **-P** and **-S** options) should be quoted to
                  protect them from expansion before the **complete** builtin is
                  invoked.
    
                  **-o** _comp-option_
                          The _comp-option_ controls several aspects of the
                          compspec's behavior beyond the simple generation of
                          completions.  _comp-option_ may be one of:
                          **bashdefault**
                                  Perform the rest of the default **bash**
                                  completions if the compspec generates no
                                  matches.
                          **default** Use **readline** 's default filename completion
                                  if the compspec generates no matches.
                          **dirnames**
                                  Perform directory name completion if the
                                  compspec generates no matches.
                          **filenames**
                                  Tell **readline** that the compspec generates
                                  filenames, so it can perform any
                                  filename-specific processing (such as
                                  adding a slash to directory names, quoting
                                  special characters, or suppressing trailing
                                  spaces).  This is intended to be used with
                                  shell functions.
                          **fullquote**
                                  Tell **readline** to quote all the completed
                                  words even if they are not filenames.
                          **noquote** Tell **readline** not to quote the completed
                                  words if they are filenames (quoting
                                  filenames is the default).
                          **nosort** Tell **readline** not to sort the list of
                                  possible completions alphabetically.
                          **nospace** Tell **readline** not to append a space (the
                                  default) to words completed at the end of
                                  the line.
                          **plusdirs**
                                  After generating any matches defined by the
                                  compspec, attempt directory name completion
                                  and add any matches to the results of the
                                  other actions.
                  **-A** _action_
                          The _action_ may be one of the following to generate
                          a list of possible completions:
                          **alias** Alias names.  May also be specified as **-a**.
                          **arrayvar**
                                  Array variable names.
                          **binding Readline** key binding names.
                          **builtin** Names of shell builtin commands.  May also
                                  be specified as **-b**.
                          **command** Command names.  May also be specified as
                                  **-c**.
                          **directory**
                                  Directory names.  May also be specified as
                                  **-d**.
                          **disabled**
                                  Names of disabled shell builtins.
                          **enabled** Names of enabled shell builtins.
                          **export** Names of exported shell variables.  May
                                  also be specified as **-e**.
                          **file** File and directory names, similar to
                                  **readline** 's filename completion.  May also
                                  be specified as **-f**.
                          **function**
                                  Names of shell functions.
                          **group** Group names.  May also be specified as **-g**.
                          **helptopic**
                                  Help topics as accepted by the **help**
                                  builtin.
                          **hostname**
                                  Hostnames, as taken from the file specified
                                  by the **HOSTFILE** shell variable.
                          **job** Job names, if job control is active.  May
                                  also be specified as **-j**.
                          **keyword** Shell reserved words.  May also be
                                  specified as **-k**.
                          **running** Names of running jobs, if job control is
                                  active.
                          **service** Service names.  May also be specified as
                                  **-s**.
                          **setopt** Valid arguments for the **-o** option to the
                                  **set** builtin.
                          **shopt** Shell option names as accepted by the **shopt**
                                  builtin.
                          **signal** Signal names.
                          **stopped** Names of stopped jobs, if job control is
                                  active.
                          **user** User names.  May also be specified as **-u**.
                          **variable**
                                  Names of all shell variables.  May also be
                                  specified as **-v**.
                  **-C** _command_
                          _command_ is executed in a subshell environment, and
                          its output is used as the possible completions.
                          Arguments are passed as with the **-F** option.
                  **-F** _function_
                          The shell function _function_ is executed in the
                          current shell environment.  When the function is
                          executed, the first argument (**$1**) is the name of
                          the command whose arguments are being completed,
                          the second argument (**$2**) is the word being
                          completed, and the third argument (**$3**) is the word
                          preceding the word being completed on the current
                          command line.  When _function_ finishes, programmable
                          completion retrieves the possible completions from
                          the value of the **COMPREPLY** array variable.
                  **-G** _globpat_
                          Expand the pathname expansion pattern _globpat_ to
                          generate the possible completions.
                  **-P** _prefix_
                          Add _prefix_ to the beginning of each possible
                          completion after all other options have been
                          applied.
                  **-S** _suffix_
                          Append _suffix_ to each possible completion after all
                          other options have been applied.
                  **-W** _wordlist_
                          Split the _wordlist_ using the characters in the **IFS**
                          special variable as delimiters, and expand each
                          resulting word.  Shell quoting is honored within
                          _wordlist_ , in order to provide a mechanism for the
                          words to contain shell metacharacters or characters
                          in the value of **IFS**.  The possible completions are
                          the members of the resultant list which match a
                          prefix of the word being completed.
                  **-X** _filterpat_
                          _filterpat_ is a pattern as used for pathname
                          expansion.  It is applied to the list of possible
                          completions generated by the preceding options and
                          arguments, and each completion matching _filterpat_
                          is removed from the list.  A leading **!** in _filterpat_
                          negates the pattern; in this case, any completion
                          not matching _filterpat_ is removed.
    
                  The return value is true unless an invalid option is
                  supplied, an option other than **-p** , **-r** , **-D** , **-E** , or **-I** is
                  supplied without a _name_ argument, an attempt is made to
                  remove a completion specification for a _name_ for which no
                  specification exists, or an error occurs adding a
                  completion specification.
    
           **compopt**[**-o** _option_] [**-DEI**] [**+o** _option_] [_name_]
                  Modify completion options for each _name_ according to the
                  _option_ s, or for the currently-executing completion if no
                  _name_ s are supplied.  If no _option_ s are supplied, display
                  the completion options for each _name_ or the current
                  completion.  The possible values of _option_ are those valid
                  for the **complete** builtin described above.
    
                  The **-D** option indicates that other supplied options should
                  apply to the “default” command completion; the **-E** option
                  indicates that other supplied options should apply to
                  “empty” command completion; and the **-I** option indicates
                  that other supplied options should apply to completion on
                  the initial word on the line.  These are determined in the
                  same way as the **complete** builtin.
    
                  If multiple options are supplied, the **-D** option takes
                  precedence over **-E** , and both take precedence over **-I**.
    
                  The return value is true unless an invalid option is
                  supplied, an attempt is made to modify the options for a
                  _name_ for which no completion specification exists, or an
                  output error occurs.
    
           **continue**[_n_]
                  **continue** resumes the next iteration of the enclosing **for** ,
                  **while** , **until** , or **select** loop.  If _n_ is specified, **bash**
                  resumes the _n_ th enclosing loop.  _n_ must be ≥ 1.  If _n_ is
                  greater than the number of enclosing loops, the shell
                  resumes the last enclosing loop (the “top-level” loop).
                  The return value is 0 unless _n_ is not greater than or equal
                  to 1.
    
           **declare**[**-aAfFgiIlnrtux**] [**-p**] [_name_[=_value_] ...]
           **typeset**[**-aAfFgiIlnrtux**] [**-p**] [_name_[=_value_] ...]
                  Declare variables and/or give them attributes.  If no _name_ s
                  are given then display the values of variables or
                  functions.  The **-p** option will display the attributes and
                  values of each _name_.  When **-p** is used with _name_ arguments,
                  additional options, other than **-f** and **-F** , are ignored.
    
                  When **-p** is supplied without _name_ arguments, **declare** will
                  display the attributes and values of all variables having
                  the attributes specified by the additional options.  If no
                  other options are supplied with **-p** , **declare** will display
                  the attributes and values of all shell variables.  The **-f**
                  option restricts the display to shell functions.
    
                  The **-F** option inhibits the display of function definitions;
                  only the function name and attributes are printed.  If the
                  **extdebug** shell option is enabled using **shopt** , the source
                  file name and line number where each _name_ is defined are
                  displayed as well.  The **-F** option implies **-f**.
    
                  The **-g** option forces variables to be created or modified at
                  the global scope, even when **declare** is executed in a shell
                  function.  It is ignored when **declare** is not executed in a
                  shell function.
    
                  The **-I** option causes local variables to inherit the
                  attributes (except the _nameref_ attribute) and value of any
                  existing variable with the same _name_ at a surrounding
                  scope.  If there is no existing variable, the local
                  variable is initially unset.
    
                  The following options can be used to restrict output to
                  variables with the specified attribute or to give variables
                  attributes:
                  **-a** Each _name_ is an indexed array variable (see **Arrays**
                         above).
                  **-A** Each _name_ is an associative array variable (see
                         **Arrays** above).
                  **-f** Each _name_ refers to a shell function.
                  **-i** The variable is treated as an integer; arithmetic
                         evaluation (see **ARITHMETIC EVALUATION** above) is
                         performed when the variable is assigned a value.
                  **-l** When the variable is assigned a value, all upper-
                         case characters are converted to lower-case.  The
                         upper-case attribute is disabled.
                  **-n** Give each _name_ the _nameref_ attribute, making it a
                         name reference to another variable.  That other
                         variable is defined by the value of _name_.  All
                         references, assignments, and attribute modifications
                         to _name_ , except those using or changing the **-n**
                         attribute itself, are performed on the variable
                         referenced by _name_ 's value.  The nameref attribute
                         cannot be applied to array variables.
                  **-r** Make _name_ s readonly.  These names cannot then be
                         assigned values by subsequent assignment statements
                         or unset.
                  **-t** Give each _name_ the _trace_ attribute.  Traced
                         functions inherit the **DEBUG** and **RETURN** traps from
                         the calling shell.  The trace attribute has no
                         special meaning for variables.
                  **-u** When the variable is assigned a value, all lower-
                         case characters are converted to upper-case.  The
                         lower-case attribute is disabled.
                  **-x** Mark each _name_ for export to subsequent commands via
                         the environment.
    
                  Using “+” instead of “-” turns off the specified attribute
                  instead, with the exceptions that **+a** and **+A** may not be used
                  to destroy array variables and **+r** will not remove the
                  readonly attribute.
    
                  When used in a function, **declare** and **typeset** make each _name_
                  local, as with the **local** command, unless the **-g** option is
                  supplied.  If a variable name is followed by =_value_ , the
                  value of the variable is set to _value_.  When using **-a** or **-A**
                  and the compound assignment syntax to create array
                  variables, additional attributes do not take effect until
                  subsequent assignments.
    
                  The return value is 0 unless an invalid option is
                  encountered, an attempt is made to define a function using
                  “-f foo=bar”, an attempt is made to assign a value to a
                  readonly variable, an attempt is made to assign a value to
                  an array variable without using the compound assignment
                  syntax (see **Arrays** above), one of the _names_ is not a valid
                  shell variable name, an attempt is made to turn off
                  readonly status for a readonly variable, an attempt is made
                  to turn off array status for an array variable, or an
                  attempt is made to display a non-existent function with **-f**.
    
           **dirs [-clpv] [+**_n_**] [-**_n_**]**
                  Without options, display the list of currently remembered
                  directories.  The default display is on a single line with
                  directory names separated by spaces.  Directories are added
                  to the list with the **pushd** command; the **popd** command
                  removes entries from the list.  The current directory is
                  always the first directory in the stack.
    
                  Options, if supplied, have the following meanings:
                  **-c** Clears the directory stack by deleting all of the
                         entries.
                  **-l** Produces a listing using full pathnames; the default
                         listing format uses a tilde to denote the home
                         directory.
                  **-p** Print the directory stack with one entry per line.
                  **-v** Print the directory stack with one entry per line,
                         prefixing each entry with its index in the stack.
                  **+**_n_     Displays the _n_ th entry counting from the left of the
                         list shown by **dirs** when invoked without options,
                         starting with zero.
                  **-**_n_     Displays the _n_ th entry counting from the right of
                         the list shown by **dirs** when invoked without options,
                         starting with zero.
    
                  The return value is 0 unless an invalid option is supplied
                  or _n_ indexes beyond the end of the directory stack.
    
           **disown**[**-ar**] [**-h**] [_id_ ...]
                  Without options, remove each _id_ from the table of active
                  jobs.  Each _id_ may be a job specification _jobspec_ or a
                  process ID _pid_ ; if _id_ is a _pid_ , **disown** uses the job
                  containing _pid_ as _jobspec_.
    
                  If the **-h** option is supplied, **disown** does not remove the
                  jobs corresponding to each _id_ from the jobs table, but
                  rather marks them so the shell does not send **SIGHUP** to the
                  job if the shell receives a **SIGHUP**.
    
                  If no _id_ is supplied, the **-a** option means to remove or mark
                  all jobs; the **-r** option without an _id_ argument removes or
                  marks running jobs.  If no _id_ is supplied, and neither the
                  **-a** nor the **-r** option is supplied, **disown** removes or marks
                  the current job.
    
                  The return value is 0 unless an _id_ does not specify a valid
                  job.
    
           **echo**[**-neE**] [_arg_ ...]
                  Output the _arg_ s, separated by spaces, followed by a
                  newline.  The return status is 0 unless a write error
                  occurs.  If **-n** is specified, the trailing newline is not
                  printed.
    
                  If the **-e** option is given, **echo** interprets the following
                  backslash-escaped characters.  The **-E** option disables
                  interpretation of these escape characters, even on systems
                  where they are interpreted by default.  The **xpg_echo** shell
                  option determines whether or not **echo** interprets any
                  options and expands these escape characters.  **echo** does not
                  interpret **--** to mean the end of options.
    
                  **echo** interprets the following escape sequences:
                  **\a** alert (bell)
                  **\b** backspace
                  **\c** suppress further output
                  **\e**
                  **\E** an escape character
                  **\f** form feed
                  **\n** new line
                  **\r** carriage return
                  **\t** horizontal tab
                  **\v** vertical tab
                  **\\** backslash
                  **\0** _nnn_  The eight-bit character whose value is the octal
                         value _nnn_ (zero to three octal digits).
                  **\x** _HH_   The eight-bit character whose value is the
                         hexadecimal value _HH_ (one or two hex digits).
                  **\u** _HHHH_ The Unicode (ISO/IEC 10646) character whose value is
                         the hexadecimal value _HHHH_ (one to four hex digits).
                  **\U** _HHHHHHHH_
                         The Unicode (ISO/IEC 10646) character whose value is
                         the hexadecimal value _HHHHHHHH_ (one to eight hex
                         digits).
    
                  **echo** writes any unrecognized backslash-escaped characters
                  unchanged.
    
           **enable**[**-a**] [**-dnps**] [**-f** _filename_] [_name_ ...]
                  Enable and disable builtin shell commands.  Disabling a
                  builtin allows an executable file which has the same name
                  as a shell builtin to be executed without specifying a full
                  pathname, even though the shell normally searches for
                  builtins before files.
    
                  If **-n** is supplied, each _name_ is disabled; otherwise, _name_ s
                  are enabled.  For example, to use the **test** binary found
                  using **PATH** instead of the shell builtin version, run
                  “enable -n test”.
    
                  If no _name_ arguments are supplied, or if the **-p** option is
                  supplied, print a list of shell builtins.  With no other
                  option arguments, the list consists of all enabled shell
                  builtins.  If **-n** is supplied, print only disabled builtins.
                  If **-a** is supplied, the list printed includes all builtins,
                  with an indication of whether or not each is enabled.  The
                  **-s** option means to restrict the output to the POSIX _special_
                  builtins.
    
                  The **-f** option means to load the new builtin command _name_
                  from shared object _filename_ , on systems that support
                  dynamic loading.  If _filename_ does not contain a slash,
                  **Bash** will use the value of the **BASH_LOADABLES_PATH** variable
                  as a colon-separated list of directories in which to search
                  for _filename_.  The default for **BASH_LOADABLES_PATH** is
                  system-dependent, and may include “.” to force a search of
                  the current directory.  The **-d** option will delete a builtin
                  previously loaded with **-f**.  If _-s_ is used with _-f_ , the new
                  builtin becomes a POSIX special builtin.
    
                  If no options are supplied and a _name_ is not a shell
                  builtin, **enable** will attempt to load _name_ from a shared
                  object named _name_ , as if the command were “enable -f _name_
                  _name_ ”.
    
                  The return value is 0 unless a _name_ is not a shell builtin
                  or there is an error loading a new builtin from a shared
                  object.
    
           **eval**[_arg_ ...]
                  Concatenate the _arg_ s together into a single command,
                  separating them with spaces.  **Bash** then reads and execute
                  this command, and returns its exit status as the return
                  status of **eval**.  If there are no _args_ , or only null
                  arguments, **eval** returns 0.
    
           **exec**[**-cl**] [**-a** _name_] [_command_ [_arguments_]]
                  If _command_ is specified, it replaces the shell without
                  creating a new process.  _command_ cannot be a shell builtin
                  or function.  The _arguments_ become the arguments to
                  _command_.  If the **-l** option is supplied, the shell places a
                  dash at the beginning of the zeroth argument passed to
                  _command_.  This is what login(1) does.  The **-c** option causes
                  _command_ to be executed with an empty environment.  If **-a** is
                  supplied, the shell passes _name_ as the zeroth argument to
                  the executed command.
    
                  If _command_ cannot be executed for some reason, a non-
                  interactive shell exits, unless the **execfail** shell option
                  is enabled.  In that case, it returns a non-zero status.
                  An interactive shell returns a non-zero status if the file
                  cannot be executed.  A subshell exits unconditionally if
                  **exec** fails.
    
                  If _command_ is not specified, any redirections take effect
                  in the current shell, and the return status is 0.  If there
                  is a redirection error, the return status is 1.
    
           **exit**[_n_]
                  Cause the shell to exit with a status of _n_.  If _n_ is
                  omitted, the exit status is that of the last command
                  executed.  Any trap on **EXIT** is executed before the shell
                  terminates.
    
           **export**[**-fn**] [_name_[=_value_]] ...
           **export -p [-f]**
                  The supplied _names_ are marked for automatic export to the
                  environment of subsequently executed commands.  If the **-f**
                  option is given, the _names_ refer to functions.
    
                  The **-n** option unexports, or removes the export attribute,
                  from each _name_.  If no _names_ are given, or if only the **-p**
                  option is supplied, **export** displays a list of names of all
                  exported variables on the standard output.  Using **-p** and **-f**
                  together displays exported functions.  The **-p** option
                  displays output in a form that may be reused as input.
    
                  **export** allows the value of a variable to be set when it is
                  exported or unexported by following the variable name with
                  =_value_.  This sets the value of the variable to _value_ while
                  modifying the export attribute.  **export** returns an exit
                  status of 0 unless an invalid option is encountered, one of
                  the _names_ is not a valid shell variable name, or **-f** is
                  supplied with a _name_ that is not a function.
    
           **false** Does nothing; returns a non-zero status.
    
           **fc**[**-e** _ename_] [**-lnr**] [_first_] [_last_]
           **fc -s**[_pat_ =_rep_] [_cmd_]
                  The first form selects a range of commands from _first_ to
                  _last_ from the history list and displays or edits and re-
                  executes them.  _First_ and _last_ may be specified as a string
                  (to locate the last command beginning with that string) or
                  as a number (an index into the history list, where a
                  negative number is used as an offset from the current
                  command number).
    
                  When listing, a _first_ or _last_ of 0 is equivalent to -1 and
                  -0 is equivalent to the current command (usually the **fc**
                  command); otherwise 0 is equivalent to -1 and -0 is
                  invalid.  If _last_ is not specified, it is set to the
                  current command for listing (so that “fc -l -10” prints the
                  last 10 commands) and to _first_ otherwise.  If _first_ is not
                  specified, it is set to the previous command for editing
                  and -16 for listing.
    
                  If the **-l** option is supplied, the commands are listed on
                  the standard output.  The **-n** option suppresses the command
                  numbers when listing.  The **-r** option reverses the order of
                  the commands.
    
                  Otherwise, **fc** invokes the editor named by _ename_ on a file
                  containing those commands.  If _ename_ is not supplied, **fc**
                  uses the value of the **FCEDIT** variable, and the value of
                  **EDITOR** if **FCEDIT** is not set.  If neither variable is set,
                  **fc** uses _vi._ When editing is complete, **fc** reads the file
                  containing the edited commands and echoes and executes
                  them.
    
                  In the second form, **fc** re-executes _command_ after replacing
                  each instance of _pat_ with _rep_.  _Command_ is interpreted the
                  same as _first_ above.
    
                  A useful alias to use with **fc** is “r="fc -s"”, so that
                  typing “r cc” runs the last command beginning with “cc” and
                  typing “r” re-executes the last command.
    
                  If the first form is used, the return value is zero unless
                  an invalid option is encountered or _first_ or _last_ specify
                  history lines out of range.  When editing and re-executing
                  a file of commands, the return value is the value of the
                  last command executed or failure if an error occurs with
                  the temporary file.  If the second form is used, the return
                  status is that of the re-executed command, unless _cmd_ does
                  not specify a valid history entry, in which case **fc** returns
                  a non-zero status.
    
           **fg**[_jobspec_]
                  Resume _jobspec_ in the foreground, and make it the current
                  job.  If _jobspec_ is not present, **fg** uses the shell's notion
                  of the _current job_.  The return value is that of the
                  command placed into the foreground, or failure if run when
                  job control is disabled or, when run with job control
                  enabled, if _jobspec_ does not specify a valid job or _jobspec_
                  specifies a job that was started without job control.
    
           **getopts** _optstring name_ [_arg_ ...]
                  **getopts** is used by shell scripts and functions to parse
                  positional parameters and obtain options and their
                  arguments.  _optstring_ contains the option characters to be
                  recognized; if a character is followed by a colon, the
                  option is expected to have an argument, which should be
                  separated from it by white space.  The colon and question
                  mark characters may not be used as option characters.
    
                  Each time it is invoked, **getopts** places the next option in
                  the shell variable _name_ , initializing _name_ if it does not
                  exist, and the index of the next argument to be processed
                  into the variable **OPTIND**.  **OPTIND** is initialized to 1 each
                  time the shell or a shell script is invoked.  When an
                  option requires an argument, **getopts** places that argument
                  into the variable **OPTARG**.
    
                  The shell does not reset **OPTIND** automatically; it must be
                  manually reset between multiple calls to **getopts** within the
                  same shell invocation to use a new set of parameters.
    
                  When it reaches the end of options, **getopts** exits with a
                  return value greater than zero.  **OPTIND** is set to the index
                  of the first non-option argument, and _name_ is set to ?.
    
                  **getopts** normally parses the positional parameters, but if
                  more arguments are supplied as _arg_ values, **getopts** parses
                  those instead.
    
                  **getopts** can report errors in two ways.  If the first
                  character of _optstring_ is a colon, **getopts** uses _silent_
                  error reporting.  In normal operation, **getopts** prints
                  diagnostic messages when it encounters invalid options or
                  missing option arguments.  If the variable **OPTERR** is set to
                  0, **getopts** does not display any error messages, even if the
                  first character of _optstring_ is not a colon.
    
                  If **getopts** detects an invalid option, it places ? into _name_
                  and, if not silent, prints an error message and unsets
                  **OPTARG**.  If **getopts** is silent, it assigns the option
                  character found to **OPTARG** and does not print a diagnostic
                  message.
    
                  If a required argument is not found, and **getopts** is not
                  silent, it sets the value of _name_ to a question mark (**?**),
                  unsets **OPTARG** , and prints a diagnostic message.  If **getopts**
                  is silent, it sets the value of _name_ to a colon (**:**) and
                  sets **OPTARG** to the option character found.
    
                  **getopts** returns true if an option, specified or
                  unspecified, is found.  It returns false if the end of
                  options is encountered or an error occurs.
    
           **hash**[**-lr**] [**-p** _filename_] [**-dt**] [_name_]
                  Each time **hash** is invoked, it remembers the full pathname
                  of the command _name_ as determined by searching the
                  directories in **$PATH**.  Any previously-remembered pathname
                  associated with _name_ is discarded.  If the **-p** option is
                  supplied, **hash** uses _filename_ as the full pathname of the
                  command.
    
                  The **-r** option causes the shell to forget all remembered
                  locations.  Assigning to the **PATH** variable also clears all
                  hashed filenames.  The **-d** option causes the shell to forget
                  the remembered location of each _name_.
    
                  If the **-t** option is supplied, **hash** prints the full pathname
                  corresponding to each _name_.  If multiple _name_ arguments are
                  supplied with **-t** , **hash** prints the _name_ before the
                  corresponding hashed full pathname.  The **-l** option displays
                  output in a format that may be reused as input.
    
                  If no arguments are given, or if only **-l** is supplied, **hash**
                  prints information about remembered commands.  The **-t** , **-d** ,
                  and **-p** options (the options that act on the _name_ arguments)
                  are mutually exclusive.  Only one will be active.  If more
                  than one is supplied, **-t** has higher priority than **-p** , and
                  both have higher priority than **-d**.
    
                  The return status is zero unless a _name_ is not found or an
                  invalid option is supplied.
    
           **help**[**-dms**] [_pattern_]
                  Display helpful information about builtin commands.  If
                  _pattern_ is specified, **help** gives detailed help on all
                  commands matching _pattern_ as described below; otherwise it
                  displays a list of all the builtins and shell compound
                  commands.
    
                  Options, if supplied, have the follow meanings:
    
                  **-d** Display a short description of each _pattern_
                  **-m** Display the description of each _pattern_ in a
                         manpage-like format
                  **-s** Display only a short usage synopsis for each _pattern_
    
                  If _pattern_ contains pattern matching characters (see
                  **Pattern Matching** above) it's treated as a shell pattern and
                  **help** prints the description of each help topic matching
                  _pattern_.
    
                  If not, and _pattern_ exactly matches the name of a help
                  topic, **help** prints the description associated with that
                  topic.  Otherwise, **help** performs prefix matching and prints
                  the descriptions of all matching help topics.
    
                  The return status is 0 unless no command matches _pattern_.
    
           **history [**_n_**]**
           **history -c**
           **history -d** _offset_
           **history -d** _start_ -_end_
           **history -anrw**[_filename_]
           **history -p** _arg_ [_arg_ ...]
           **history -s** _arg_ [_arg_ ...]
                  With no options, display the command history list with
                  numbers.  Entries prefixed with a ***** have been modified.  An
                  argument of _n_ lists only the last _n_ entries.  If the shell
                  variable **HISTTIMEFORMAT** is set and not null, it is used as
                  a format string for strftime(3) to display the time stamp
                  associated with each displayed history entry.  If **history**
                  uses **HISTTIMEFORMAT** , it does not print an intervening space
                  between the formatted time stamp and the history entry.
    
                  If _filename_ is supplied, **history** uses it as the name of the
                  history file; if not, it uses the value of **HISTFILE**.  If
                  _filename_ is not supplied and **HISTFILE** is unset or null, the
                  **-a, -n, -r,** and **-w** options have no effect.
    
                  Options, if supplied, have the following meanings:
                  **-c** Clear the history list by deleting all the entries.
                         This can be used with the other options to replace
                         the history list.
                  **-d** _offset_
                         Delete the history entry at position _offset_.  If
                         _offset_ is negative, it is interpreted as relative to
                         one greater than the last history position, so
                         negative indices count back from the end of the
                         history, and an index of -1 refers to the current
                         **history -d** command.
                  **-d** _start_ -_end_
                         Delete the range of history entries between
                         positions _start_ and _end_ , inclusive.  Positive and
                         negative values for _start_ and _end_ are interpreted as
                         described above.
                  **-a** Append the “new” history lines to the history file.
                         These are history lines entered since the beginning
                         of the current **bash** session, but not already
                         appended to the history file.
                  **-n** Read the history lines not already read from the
                         history file and add them to the current history
                         list.  These are lines appended to the history file
                         since the beginning of the current **bash** session.
                  **-r** Read the history file and append its contents to the
                         current history list.
                  **-w** Write the current history list to the history file,
                         overwriting the history file.
                  **-p** Perform history substitution on the following _args_
                         and display the result on the standard output,
                         without storing the results in the history list.
                         Each _arg_ must be quoted to disable normal history
                         expansion.
                  **-s** Store the _args_ in the history list as a single
                         entry.  The last command in the history list is
                         removed before adding the _args_.
    
                  If the **HISTTIMEFORMAT** variable is set, **history** writes the
                  time stamp information associated with each history entry
                  to the history file, marked with the history comment
                  character as described above.  When the history file is
                  read, lines beginning with the history comment character
                  followed immediately by a digit are interpreted as
                  timestamps for the following history entry.
    
                  The return value is 0 unless an invalid option is
                  encountered, an error occurs while reading or writing the
                  history file, an invalid _offset_ or range is supplied as an
                  argument to **-d** , or the history expansion supplied as an
                  argument to **-p** fails.
    
           **jobs**[**-lnprs**] [ _jobspec_ ... ]
           **jobs -x** _command_ [ _args_ ... ]
                  The first form lists the active jobs.  The options have the
                  following meanings:
                  **-l** List process IDs in addition to the normal
                         information.
                  **-n** Display information only about jobs that have
                         changed status since the user was last notified of
                         their status.
                  **-p** List only the process ID of the job's process group
                         leader.
                  **-r** Display only running jobs.
                  **-s** Display only stopped jobs.
    
                  If _jobspec_ is supplied, **jobs** restricts output to
                  information about that job.  The return status is 0 unless
                  an invalid option is encountered or an invalid _jobspec_ is
                  supplied.
    
                  If the **-x** option is supplied, **jobs** replaces any _jobspec_
                  found in _command_ or _args_ with the corresponding process
                  group ID, and executes _command_ , passing it _args_ , returning
                  its exit status.
    
           **kill**[**-s** _sigspec_ | **-n** _signum_ | **-**_sigspec_] _id_ [ ... ]
           **kill -l** |**-L**[_sigspec_ | _exit_status_]
                  Send the signal specified by _sigspec_ or _signum_ to the
                  processes named by each _id_.  Each _id_ may be a job
                  specification _jobspec_ or a process ID _pid_.  _sigspec_ is
                  either a case-insensitive signal name such as **SIGKILL**(with
                  or without the **SIG** prefix) or a signal number; _signum_ is a
                  signal number.  If _sigspec_ is not supplied, then **kill** sends
                  **SIGTERM**.
    
                  The **-l** option lists the signal names.  If any arguments are
                  supplied when **-l** is given, **kill** lists the names of the
                  signals corresponding to the arguments, and the return
                  status is 0.  The _exit_status_ argument to **-l** is a number
                  specifying either a signal number or the exit status of a
                  process terminated by a signal; if it is supplied, **kill**
                  prints the name of the signal that caused the process to
                  terminate.  **kill** assumes that process exit statuses are
                  greater than 128; anything less than that is a signal
                  number.  The **-L** option is equivalent to **-l**.
    
                  **kill** returns true if at least one signal was successfully
                  sent, or false if an error occurs or an invalid option is
                  encountered.
    
           **let** _arg_ [_arg_ ...]
                  Each _arg_ is evaluated as an arithmetic expression (see
                  **ARITHMETIC EVALUATION** above).  If the last _arg_ evaluates to
                  0, **let** returns 1; otherwise **let** returns 0.
    
           **local**[_option_] [_name_[=_value_] ... | - ]
                  For each argument, create a local variable named _name_ and
                  assign it _value_.  The _option_ can be any of the options
                  accepted by **declare**.  When **local** is used within a function,
                  it causes the variable _name_ to have a visible scope
                  restricted to that function and its children.  It is an
                  error to use **local** when not within a function.
    
                  If _name_ is -, it makes the set of shell options local to
                  the function in which **local** is invoked: any shell options
                  changed using the **set** builtin inside the function after the
                  call to **local** are restored to their original values when
                  the function returns.  The restore is performed as if a
                  series of **set** commands were executed to restore the values
                  that were in place before the function.
    
                  With no operands, **local** writes a list of local variables to
                  the standard output.
    
                  The return status is 0 unless **local** is used outside a
                  function, an invalid _name_ is supplied, or _name_ is a
                  readonly variable.
    
           **logout [**_n_**]**
                  Exit a login shell, returning a status of _n_ to the shell's
                  parent.
    
           **mapfile**[**-d** _delim_] [**-n** _count_] [**-O** _origin_] [**-s** _count_] [**-t**] [**-u** _fd_]
           [**-C** _callback_] [**-c** _quantum_] [_array_]
           **readarray**[**-d** _delim_] [**-n** _count_] [**-O** _origin_] [**-s** _count_] [**-t**] [**-u**
           _fd_] [**-C** _callback_] [**-c** _quantum_] [_array_]
                  Read lines from the standard input, or from file descriptor
                  _fd_ if the **-u** option is supplied, into the indexed array
                  variable _array_.  The variable **MAPFILE** is the default _array_.
                  Options, if supplied, have the following meanings:
                  **-d** Use the first character of _delim_ to terminate each
                         input line, rather than newline.  If _delim_ is the
                         empty string, **mapfile** will terminate a line when it
                         reads a NUL character.
                  **-n** Copy at most _count_ lines.  If _count_ is 0, copy all
                         lines.
                  **-O** Begin assigning to _array_ at index _origin_.  The
                         default index is 0.
                  **-s** Discard the first _count_ lines read.
                  **-t** Remove a trailing _delim_ (default newline) from each
                         line read.
                  **-u** Read lines from file descriptor _fd_ instead of the
                         standard input.
                  **-C** Evaluate _callback_ each time _quantum_ lines are read.
                         The **-c** option specifies _quantum_.
                  **-c** Specify the number of lines read between each call
                         to _callback_.
    
                  If **-C** is specified without **-c** , the default quantum is 5000.
                  When _callback_ is evaluated, it is supplied the index of the
                  next array element to be assigned and the line to be
                  assigned to that element as additional arguments.  _callback_
                  is evaluated after the line is read but before the array
                  element is assigned.
    
                  If not supplied with an explicit origin, **mapfile** will clear
                  _array_ before assigning to it.
    
                  **mapfile** returns zero unless an invalid option or option
                  argument is supplied, _array_ is invalid or unassignable, or
                  if _array_ is not an indexed array.
    
           **popd**[-**n**] [+_n_] [-_n_]
                  Remove entries from the directory stack.  The elements are
                  numbered from 0 starting at the first directory listed by
                  **dirs** , so **popd** is equivalent to “popd +0.”  With no
                  arguments, **popd** removes the top directory from the stack,
                  and changes to the new top directory.  Arguments, if
                  supplied, have the following meanings:
                  **-n** Suppress the normal change of directory when
                         removing directories from the stack, only manipulate
                         the stack.
                  **+**_n_     Remove the _n_ th entry counting from the left of the
                         list shown by **dirs** , starting with zero, from the
                         stack.  For example: “popd +0” removes the first
                         directory, “popd +1” the second.
                  **-**_n_     Remove the _n_ th entry counting from the right of the
                         list shown by **dirs** , starting with zero.  For
                         example: “popd -0” removes the last directory, “popd
                         -1” the next to last.
    
                  If the top element of the directory stack is modified, and
                  the _-n_ option was not supplied, **popd** uses the **cd** builtin to
                  change to the directory at the top of the stack.  If the **cd**
                  fails, **popd** returns a non-zero value.
    
                  Otherwise, **popd** returns false if an invalid option is
                  supplied, the directory stack is empty, or _n_ specifies a
                  non-existent directory stack entry.
    
                  If the **popd** command is successful, **bash** runs **dirs** to show
                  the final contents of the directory stack, and the return
                  status is 0.
    
           **printf**[**-v** _var_] _format_ [_arguments_]
                  Write the formatted _arguments_ to the standard output under
                  the control of the _format_.  The **-v** option assigns the
                  output to the variable _var_ rather than printing it to the
                  standard output.
    
                  The _format_ is a character string which contains three types
                  of objects: plain characters, which are simply copied to
                  standard output, character escape sequences, which are
                  converted and copied to the standard output, and format
                  specifications, each of which causes printing of the next
                  successive _argument_.  In addition to the standard printf(3)
                  format characters **cCsSndiouxXeEfFgGaA** , **printf** interprets
                  the following additional format specifiers:
                  **%b** causes **printf** to expand backslash escape sequences
                         in the corresponding _argument_ in the same way as
                         **echo -e**.
                  **%q** causes **printf** to output the corresponding _argument_
                         in a format that can be reused as shell input.  **%q**
                         and **%Q** use the **$''** quoting style if any characters
                         in the argument string require it, and backslash
                         quoting otherwise.  If the format string uses the
                         _printf_ alternate form, these two formats quote the
                         argument string using single quotes.
                  **%Q** like **%q** , but applies any supplied precision to the
                         _argument_ before quoting it.
                  **%(**_datefmt_**)T**
                         causes **printf** to output the date-time string
                         resulting from using _datefmt_ as a format string for
                         strftime(3).  The corresponding _argument_ is an
                         integer representing the number of seconds since the
                         epoch.  This format specifier recognizes two special
                         argument values: -1 represents the current time, and
                         -2 represents the time the shell was invoked.  If no
                         argument is specified, conversion behaves as if -1
                         had been supplied.  This is an exception to the
                         usual **printf** behavior.
    
                  The %b, %q, and %T format specifiers all use the field
                  width and precision arguments from the format specification
                  and write that many bytes from (or use that wide a field
                  for) the expanded argument, which usually contains more
                  characters than the original.
    
                  The %n format specifier accepts a corresponding argument
                  that is treated as a shell variable name.
    
                  The %s and %c format specifiers accept an l (long)
                  modifier, which forces them to convert the argument string
                  to a wide-character string and apply any supplied field
                  width and precision in terms of characters, not bytes.  The
                  %S and %C format specifiers are equivalent to %ls and %lc,
                  respectively.
    
                  Arguments to non-string format specifiers are treated as C
                  constants, except that a leading plus or minus sign is
                  allowed, and if the leading character is a single or double
                  quote, the value is the numeric value of the following
                  character, using the current locale.
    
                  The _format_ is reused as necessary to consume all of the
                  _arguments_.  If the _format_ requires more _arguments_ than are
                  supplied, the extra format specifications behave as if a
                  zero value or null string, as appropriate, had been
                  supplied.  The return value is zero on success, non-zero if
                  an invalid option is supplied or a write or assignment
                  error occurs.
    
           **pushd**[**-n**] [+_n_] [-_n_]
           **pushd**[**-n**] [_dir_]
                  Add a directory to the top of the directory stack, or
                  rotate the stack, making the new top of the stack the
                  current working directory.  With no arguments, **pushd**
                  exchanges the top two elements of the directory stack.
                  Arguments, if supplied, have the following meanings:
                  **-n** Suppress the normal change of directory when
                         rotating or adding directories to the stack, only
                         manipulate the stack.
                  **+**_n_     Rotate the stack so that the _n_ th directory (counting
                         from the left of the list shown by **dirs** , starting
                         with zero) is at the top.
                  **-**_n_     Rotates the stack so that the _n_ th directory
                         (counting from the right of the list shown by **dirs** ,
                         starting with zero) is at the top.
                  _dir_    Adds _dir_ to the directory stack at the top.
    
                  After the stack has been modified, if the **-n** option was not
                  supplied, **pushd** uses the **cd** builtin to change to the
                  directory at the top of the stack.  If the **cd** fails, **pushd**
                  returns a non-zero value.
    
                  Otherwise, if no arguments are supplied, **pushd** returns zero
                  unless the directory stack is empty.  When rotating the
                  directory stack, **pushd** returns zero unless the directory
                  stack is empty or _n_ specifies a non-existent directory
                  stack element.
    
                  If the **pushd** command is successful, **bash** runs **dirs** to show
                  the final contents of the directory stack.
    
           **pwd**[**-LP**]
                  Print the absolute pathname of the current working
                  directory.  The pathname printed contains no symbolic links
                  if the **-P** option is supplied or the **-o physical** option to
                  the **set** builtin command is enabled.  If the **-L** option is
                  used, the pathname printed may contain symbolic links.  The
                  return status is 0 unless an error occurs while reading the
                  name of the current directory or an invalid option is
                  supplied.
    
           **read**[**-Eers**] [**-a** _aname_] [**-d** _delim_] [**-i** _text_] [**-n** _nchars_] [**-N**
           _nchars_] [**-p** _prompt_] [**-t** _timeout_] [**-u** _fd_] [_name_ ...]
                  Read one line from the standard input, or from the file
                  descriptor _fd_ supplied as an argument to the **-u** option,
                  split it into words as described above under **Word**
                  **Splitting** , and assign the first word to the first _name_ , the
                  second word to the second _name_ , and so on.  If there are
                  more words than names, the remaining words and their
                  intervening delimiters are assigned to the last _name_.  If
                  there are fewer words read from the input stream than
                  names, the remaining names are assigned empty values.  The
                  characters in the value of the **IFS** variable are used to
                  split the line into words using the same rules the shell
                  uses for expansion (described above under **Word Splitting**).
                  The backslash character (**\**) removes any special meaning for
                  the next character read and is used for line continuation.
    
                  Options, if supplied, have the following meanings:
                  **-a** _aname_
                         The words are assigned to sequential indices of the
                         array variable _aname_ , starting at 0.  _aname_ is unset
                         before any new values are assigned.  Other _name_
                         arguments are ignored.
                  **-d** _delim_
                         The first character of _delim_ terminates the input
                         line, rather than newline.  If _delim_ is the empty
                         string, **read** will terminate a line when it reads a
                         NUL character.
                  **-e** If the standard input is coming from a terminal,
                         **read** uses **readline**(see **READLINE** above) to obtain
                         the line.  **Readline** uses the current (or default, if
                         line editing was not previously active) editing
                         settings, but uses **readline** 's default filename
                         completion.
                  **-E** If the standard input is coming from a terminal,
                         **read** uses **readline**(see **READLINE** above) to obtain
                         the line.  **Readline** uses the current (or default, if
                         line editing was not previously active) editing
                         settings, but uses bash's default completion,
                         including programmable completion.
                  **-i** _text_
                         If **readline** is being used to read the line, **read**
                         places _text_ into the editing buffer before editing
                         begins.
                  **-n** _nchars_
                         **read** returns after reading _nchars_ characters rather
                         than waiting for a complete line of input, unless it
                         encounters EOF or **read** times out, but honors a
                         delimiter if it reads fewer than _nchars_ characters
                         before the delimiter.
                  **-N** _nchars_
                         **read** returns after reading exactly _nchars_ characters
                         rather than waiting for a complete line of input,
                         unless it encounters EOF or **read** times out.  Any
                         delimiter characters in the input are not treated
                         specially and do not cause **read** to return until it
                         has read _nchars_ characters.  The result is not split
                         on the characters in **IFS** ; the intent is that the
                         variable is assigned exactly the characters read
                         (with the exception of backslash; see the **-r** option
                         below).
                  **-p** _prompt_
                         Display _prompt_ on standard error, without a trailing
                         newline, before attempting to read any input, but
                         only if input is coming from a terminal.
                  **-r** Backslash does not act as an escape character.  The
                         backslash is considered to be part of the line.  In
                         particular, a backslash-newline pair may not then be
                         used as a line continuation.
                  **-s** Silent mode.  If input is coming from a terminal,
                         characters are not echoed.
                  **-t** _timeout_
                         Cause **read** to time out and return failure if it does
                         not read a complete line of input (or a specified
                         number of characters) within _timeout_ seconds.
                         _timeout_ may be a decimal number with a fractional
                         portion following the decimal point.  This option is
                         only effective if **read** is reading input from a
                         terminal, pipe, or other special file; it has no
                         effect when reading from regular files.  If **read**
                         times out, it saves any partial input read into the
                         specified variable _name_ , and the exit status is
                         greater than 128.  If _timeout_ is 0, **read** returns
                         immediately, without trying to read any data.  In
                         this case, the exit status is 0 if input is
                         available on the specified file descriptor, or the
                         read will return EOF, non-zero otherwise.
                  **-u** _fd_  Read input from file descriptor _fd_ instead of the
                         standard input.
    
                  Other than the case where _delim_ is the empty string, **read**
                  ignores any NUL characters in the input.
    
                  If no _names_ are supplied, **read** assigns the line read,
                  without the ending delimiter but otherwise unmodified, to
                  the variable **REPLY**.
    
                  The exit status is zero, unless end-of-file is encountered,
                  **read** times out (in which case the status is greater than
                  128), a variable assignment error (such as assigning to a
                  readonly variable) occurs, or an invalid file descriptor is
                  supplied as the argument to **-u**.
    
           **readonly**[**-aAf**] [**-p**] [_name_[=_word_] ...]
                  The given _names_ are marked readonly; the values of these
                  _names_ may not be changed by subsequent assignment or unset.
                  If the **-f** option is supplied, each _name_ refers to a shell
                  function.  The **-a** option restricts the variables to indexed
                  arrays; the **-A** option restricts the variables to
                  associative arrays.  If both options are supplied, **-A** takes
                  precedence.  If no _name_ arguments are supplied, or if the
                  **-p** option is supplied, print a list of all readonly names.
                  The other options may be used to restrict the output to a
                  subset of the set of readonly names.  The **-p** option
                  displays output in a format that may be reused as input.
    
                  **readonly** allows the value of a variable to be set at the
                  same time the readonly attribute is changed by following
                  the variable name with =_value_.  This sets the value of the
                  variable is to _value_ while modifying the readonly
                  attribute.
    
                  The return status is 0 unless an invalid option is
                  encountered, one of the _names_ is not a valid shell variable
                  name, or **-f** is supplied with a _name_ that is not a function.
    
           **return**[_n_]
                  Stop executing a shell function or sourced file and return
                  the value specified by _n_ to its caller.  If _n_ is omitted,
                  the return status is that of the last command executed.  If
                  **return** is executed by a trap handler, the last command used
                  to determine the status is the last command executed before
                  the trap handler.  If **return** is executed during a **DEBUG**
                  trap, the last command used to determine the status is the
                  last command executed by the trap handler before **return** was
                  invoked.
    
                  When **return** is used to terminate execution of a script
                  being executed by the **.**(**source**) command, it causes the
                  shell to stop executing that script and return either _n_ or
                  the exit status of the last command executed within the
                  script as the exit status of the script.  If _n_ is supplied,
                  the return value is its least significant 8 bits.
    
                  Any command associated with the **RETURN** trap is executed
                  before execution resumes after the function or script.
    
                  The return status is non-zero if **return** is supplied a non-
                  numeric argument, or is used outside a function and not
                  during execution of a script by **.** or **source**.
    
           **set**[**-abefhkmnptuvxBCEHPT**] [**-o** _option-name_] [**--**] [**-**] [_arg_ ...]
           **set**[**+abefhkmnptuvxBCEHPT**] [**+o** _option-name_] [**--**] [**-**] [_arg_ ...]
           **set -o**
           **set +o** Without options, display the name and value of each shell
                  variable in a format that can be reused as input for
                  setting or resetting the currently-set variables.  Read-
                  only variables cannot be reset.  In posix mode, only shell
                  variables are listed.  The output is sorted according to
                  the current locale.  When options are specified, they set
                  or unset shell attributes.  Any arguments remaining after
                  option processing are treated as values for the positional
                  parameters and are assigned, in order, to **$1** , **$2** , ..., **$**_n_.
                  Options, if specified, have the following meanings:
                  **-a** Each variable or function that is created or
                          modified is given the export attribute and marked
                          for export to the environment of subsequent
                          commands.
                  **-b** Report the status of terminated background jobs
                          immediately, rather than before the next primary
                          prompt or after a foreground command terminates.
                          This is effective only when job control is enabled.
                  **-e** Exit immediately if a _pipeline_ (which may consist
                          of a single _simple command_), a _list_ , or a _compound_
                          _command_ (see **SHELL GRAMMAR** above), exits with a
                          non-zero status.  The shell does not exit if the
                          command that fails is part of the command list
                          immediately following a **while** or **until** reserved
                          word, part of the test following the **if** or **elif**
                          reserved words, part of any command executed in a
                          **& & **or **||** list except the command following the
                          final **& & **or **||** , any command in a pipeline but the
                          last (subject to the state of the **pipefail** shell
                          option), or if the command's return value is being
                          inverted with **!**.  If a compound command other than
                          a subshell returns a non-zero status because a
                          command failed while **-e** was being ignored, the
                          shell does not exit.  A trap on **ERR** , if set, is
                          executed before the shell exits.  This option
                          applies to the shell environment and each subshell
                          environment separately (see **COMMAND EXECUTION**
                          **ENVIRONMENT** above), and may cause subshells to exit
                          before executing all the commands in the subshell.
    
                          If a compound command or shell function executes in
                          a context where **-e** is being ignored, none of the
                          commands executed within the compound command or
                          function body will be affected by the **-e** setting,
                          even if **-e** is set and a command returns a failure
                          status.  If a compound command or shell function
                          sets **-e** while executing in a context where **-e** is
                          ignored, that setting will not have any effect
                          until the compound command or the command
                          containing the function call completes.
                  **-f** Disable pathname expansion.
                  **-h** Remember the location of commands as they are
                          looked up for execution.  This is enabled by
                          default.
                  **-k** All arguments in the form of assignment statements
                          are placed in the environment for a command, not
                          just those that precede the command name.
                  **-m** Monitor mode.  Job control is enabled.  This option
                          is on by default for interactive shells on systems
                          that support it (see **JOB CONTROL** above).  All
                          processes run in a separate process group.  When a
                          background job completes, the shell prints a line
                          containing its exit status.
                  **-n** Read commands but do not execute them.  This may be
                          used to check a shell script for syntax errors.
                          This is ignored by interactive shells.
                  **-o** _option-name_
                          The _option-name_ can be one of the following:
                          **allexport**
                                  Same as **-a**.
                          **braceexpand**
                                  Same as **-B**.
                          **emacs** Use an emacs-style command line editing
                                  interface.  This is enabled by default when
                                  the shell is interactive, unless the shell
                                  is started with the **--noediting** option.
                                  This also affects the editing interface
                                  used for **read -e**.
                          **errexit** Same as **-e**.
                          **errtrace**
                                  Same as **-E**.
                          **functrace**
                                  Same as **-T**.
                          **hashall** Same as **-h**.
                          **histexpand**
                                  Same as **-H**.
                          **history** Enable command history, as described above
                                  under **HISTORY**.  This option is on by
                                  default in interactive shells.
                          **ignoreeof**
                                  The effect is as if the shell command
                                  “IGNOREEOF=10” had been executed (see **Shell**
                                  **Variables** above).
                          **keyword** Same as **-k**.
                          **monitor** Same as **-m**.
                          **noclobber**
                                  Same as **-C**.
                          **noexec** Same as **-n**.
                          **noglob** Same as **-f**.
                          **nolog** Currently ignored.
                          **notify** Same as **-b**.
                          **nounset** Same as **-u**.
                          **onecmd** Same as **-t**.
                          **physical**
                                  Same as **-P**.
                          **pipefail**
                                  If set, the return value of a pipeline is
                                  the value of the last (rightmost) command
                                  to exit with a non-zero status, or zero if
                                  all commands in the pipeline exit
                                  successfully.  This option is disabled by
                                  default.
                          **posix** Enable posix mode; change the behavior of
                                  **bash** where the default operation differs
                                  from the POSIX standard to match the
                                  standard.  See **SEE ALSO** below for a
                                  reference to a document that details how
                                  posix mode affects bash's behavior.
                          **privileged**
                                  Same as **-p**.
                          **verbose** Same as **-v**.
                          **vi** Use a vi-style command line editing
                                  interface.  This also affects the editing
                                  interface used for **read -e**.
                          **xtrace** Same as **-x**.
                          If **-o** is supplied with no _option-name_ , **set** prints
                          the current shell option settings.  If **+o** is
                          supplied with no _option-name_ , **set** prints a series
                          of **set** commands to recreate the current option
                          settings on the standard output.
                  **-p** Turn on _privileged_ mode.  In this mode, the shell
                          does not read the **$ENV** and **$BASH_ENV** files, shell
                          functions are not inherited from the environment,
                          and the **SHELLOPTS** , **BASHOPTS** , **CDPATH** , and **GLOBIGNORE**
                          variables, if they appear in the environment, are
                          ignored.  If the shell is started with the
                          effective user (group) id not equal to the real
                          user (group) id, and the **-p** option is not supplied,
                          these actions are taken and the effective user id
                          is set to the real user id.  If the **-p** option is
                          supplied at startup, the effective user id is not
                          reset.  Turning this option off causes the
                          effective user and group ids to be set to the real
                          user and group ids.
                  **-r** Enable restricted shell mode.  This option cannot
                          be unset once it has been set.
                  **-t** Exit after reading and executing one command.
                  **-u** Treat unset variables and parameters other than the
                          special parameters “@” and “*”, or array variables
                          subscripted with “@” or “*”, as an error when
                          performing parameter expansion.  If expansion is
                          attempted on an unset variable or parameter, the
                          shell prints an error message, and, if not
                          interactive, exits with a non-zero status.
                  **-v** Print shell input lines as they are read.
                  **-x** After expanding each _simple command_ , **for** command,
                          **case** command, **select** command, or arithmetic **for**
                          command, display the expanded value of **PS4** ,
                          followed by the command and its expanded arguments
                          or associated word list, to the standard error.
                  **-B** The shell performs brace expansion (see **Brace**
                          **Expansion** above).  This is on by default.
                  **-C** If set, **bash** does not overwrite an existing file
                          with the **>** , **> &**, and **< > **redirection operators.
                          Using the redirection operator **> | **instead of **> **will
                          override this and force the creation of an output
                          file.
                  **-E** If set, any trap on **ERR** is inherited by shell
                          functions, command substitutions, and commands
                          executed in a subshell environment.  The **ERR** trap
                          is normally not inherited in such cases.
                  **-H** Enable **!** style history substitution.  This option
                          is on by default when the shell is interactive.
                  **-P** If set, the shell does not resolve symbolic links
                          when executing commands such as **cd** that change the
                          current working directory.  It uses the physical
                          directory structure instead.  By default, **bash**
                          follows the logical chain of directories when
                          performing commands which change the current
                          directory.
                  **-T** If set, any traps on **DEBUG** and **RETURN** are inherited
                          by shell functions, command substitutions, and
                          commands executed in a subshell environment.  The
                          **DEBUG** and **RETURN** traps are normally not inherited
                          in such cases.
                  **--** If no arguments follow this option, unset the
                          positional parameters.  Otherwise, set the
                          positional parameters to the _arg_ s, even if some of
                          them begin with a **-**.
                  **-** Signal the end of options, and assign all remaining
                          _arg_ s to the positional parameters.  The **-x** and **-v**
                          options are turned off.  If there are no _arg_ s, the
                          positional parameters remain unchanged.
    
                  The options are off by default unless otherwise noted.
                  Using + rather than - causes these options to be turned
                  off.  The options can also be specified as arguments to an
                  invocation of the shell.  The current set of options may be
                  found in **$-**.  The return status is always zero unless an
                  invalid option is encountered.
    
           **shift**[_n_]
                  Rename positional parameters from _n_ +1 ... to **$1 ....**
                  Parameters represented by the numbers **$#** down to **$#** -_n_ +1 are
                  unset.  _n_ must be a non-negative number less than or equal
                  to **$#**.  If _n_ is 0, no parameters are changed.  If _n_ is not
                  given, it is assumed to be 1.  If _n_ is greater than **$#** , the
                  positional parameters are not changed.  The return status
                  is greater than zero if _n_ is greater than **$#** or less than
                  zero; otherwise 0.
    
           **shopt**[**-pqsu**] [**-o**] [_optname_ ...]
                  Toggle the values of settings controlling optional shell
                  behavior.  The settings can be either those listed below,
                  or, if the **-o** option is used, those available with the **-o**
                  option to the **set** builtin command.
    
                  With no options, or with the **-p** option, display a list of
                  all settable options, with an indication of whether or not
                  each is set; if any _optnames_ are supplied, the output is
                  restricted to those options.  The **-p** option displays output
                  in a form that may be reused as input.
    
                  Other options have the following meanings:
                  **-s** Enable (set) each _optname_.
                  **-u** Disable (unset) each _optname_.
                  **-q** Suppresses normal output (quiet mode); the return
                         status indicates whether the _optname_ is set or
                         unset.  If multiple _optname_ arguments are supplied
                         with **-q** , the return status is zero if all _optnames_
                         are enabled; non-zero otherwise.
                  **-o** Restricts the values of _optname_ to be those defined
                         for the **-o** option to the **set** builtin.
    
                  If either **-s** or **-u** is used with no _optname_ arguments, **shopt**
                  shows only those options which are set or unset,
                  respectively.  Unless otherwise noted, the **shopt** options
                  are disabled (unset) by default.
    
                  The return status when listing options is zero if all
                  _optnames_ are enabled, non-zero otherwise.  When setting or
                  unsetting options, the return status is zero unless an
                  _optname_ is not a valid shell option.
    
                  The list of **shopt** options is:
    
                  **array_expand_once**
                          If set, the shell suppresses multiple evaluation of
                          associative and indexed array subscripts during
                          arithmetic expression evaluation, while executing
                          builtins that can perform variable assignments, and
                          while executing builtins that perform array
                          dereferencing.
                  **assoc_expand_once**
                          Deprecated; a synonym for **array_expand_once**.
                  **autocd** If set, a command name that is the name of a
                          directory is executed as if it were the argument to
                          the **cd** command.  This option is only used by
                          interactive shells.
                  **bash_source_fullpath**
                          If set, filenames added to the **BASH_SOURCE** array
                          variable are converted to full pathnames (see **Shell**
                          **Variables** above).
                  **cdable_vars**
                          If set, an argument to the **cd** builtin command that
                          is not a directory is assumed to be the name of a
                          variable whose value is the directory to change to.
                  **cdspell** If set, the **cd** command attempts to correct minor
                          errors in the spelling of a directory component.
                          Minor errors include transposed characters, a
                          missing character, and one extra character.  If **cd**
                          corrects the directory name, it prints the
                          corrected filename, and the command proceeds.  This
                          option is only used by interactive shells.
                  **checkhash**
                          If set, **bash** checks that a command found in the
                          hash table exists before trying to execute it.  If
                          a hashed command no longer exists, **bash** performs a
                          normal path search.
                  **checkjobs**
                          If set, **bash** lists the status of any stopped and
                          running jobs before exiting an interactive shell.
                          If any jobs are running, **bash** defers the exit until
                          a second exit is attempted without an intervening
                          command (see **JOB CONTROL** above).  The shell always
                          postpones exiting if any jobs are stopped.
                  **checkwinsize**
                          If set, **bash** checks the window size after each
                          external (non-builtin) command and, if necessary,
                          updates the values of **LINES** and **COLUMNS** , using the
                          file descriptor associated with the standard error
                          if it is a terminal.  This option is enabled by
                          default.
                  **cmdhist** If set, **bash** attempts to save all lines of a
                          multiple-line command in the same history entry.
                          This allows easy re-editing of multi-line commands.
                          This option is enabled by default, but only has an
                          effect if command history is enabled, as described
                          above under **HISTORY**.
                  **compat31**
                  **compat32**
                  **compat40**
                  **compat41**
                  **compat42**
                  **compat43**
                  **compat44**
                          These control aspects of the shell's compatibility
                          mode (see **SHELL COMPATIBILITY MODE** below).
                  **complete_fullquote**
                          If set, **bash** quotes all shell metacharacters in
                          filenames and directory names when performing
                          completion.  If not set, **bash** removes
                          metacharacters such as the dollar sign from the set
                          of characters that will be quoted in completed
                          filenames when these metacharacters appear in shell
                          variable references in words to be completed.  This
                          means that dollar signs in variable names that
                          expand to directories will not be quoted; however,
                          any dollar signs appearing in filenames will not be
                          quoted, either.  This is active only when bash is
                          using backslashes to quote completed filenames.
                          This variable is set by default, which is the
                          default bash behavior in versions through 4.2.
                  **direxpand**
                          If set, **bash** replaces directory names with the
                          results of word expansion when performing filename
                          completion.  This changes the contents of the
                          **readline** editing buffer.  If not set, **bash** attempts
                          to preserve what the user typed.
                  **dirspell**
                          If set, **bash** attempts spelling correction on
                          directory names during word completion if the
                          directory name initially supplied does not exist.
                  **dotglob** If set, **bash** includes filenames beginning with a
                          “.” in the results of pathname expansion.  The
                          filenames _._ and _.._ must always be matched
                          explicitly, even if **dotglob** is set.
                  **execfail**
                          If set, a non-interactive shell will not exit if it
                          cannot execute the file specified as an argument to
                          the **exec** builtin.  An interactive shell does not
                          exit if **exec** fails.
                  **expand_aliases**
                          If set, aliases are expanded as described above
                          under **ALIASES**.  This option is enabled by default
                          for interactive shells.
                  **extdebug**
                          If set at shell invocation, or in a shell startup
                          file, arrange to execute the debugger profile
                          before the shell starts, identical to the
                          **--debugger** option.  If set after invocation,
                          behavior intended for use by debuggers is enabled:
                          **1.** The **-F** option to the **declare** builtin
                                 displays the source file name and line
                                 number corresponding to each function name
                                 supplied as an argument.
                          **2.** If the command run by the **DEBUG** trap returns
                                 a non-zero value, the next command is
                                 skipped and not executed.
                          **3.** If the command run by the **DEBUG** trap returns
                                 a value of 2, and the shell is executing in
                                 a subroutine (a shell function or a shell
                                 script executed by the **.** or **source**
                                 builtins), the shell simulates a call to
                                 **return**.
                          **4.     BASH_ARGC** and **BASH_ARGV** are updated as
                                 described in their descriptions above).
                          **5.** Function tracing is enabled: command
                                 substitution, shell functions, and subshells
                                 invoked with **(**_command_ **)** inherit the **DEBUG**
                                 and **RETURN** traps.
                          **6.** Error tracing is enabled: command
                                 substitution, shell functions, and subshells
                                 invoked with **(**_command_ **)** inherit the **ERR**
                                 trap.
                  **extglob** If set, enable the extended pattern matching
                          features described above under **Pathname Expansion**.
                  **extquote**
                          If set, **$** '_string_ ' and **$** "_string_ " quoting is
                          performed within **${**_parameter_**}** expansions enclosed
                          in double quotes.  This option is enabled by
                          default.
                  **failglob**
                          If set, patterns which fail to match filenames
                          during pathname expansion result in an expansion
                          error.
                  **force_fignore**
                          If set, the suffixes specified by the **FIGNORE** shell
                          variable cause words to be ignored when performing
                          word completion even if the ignored words are the
                          only possible completions.  See **Shell Variables**
                          above for a description of **FIGNORE**.  This option is
                          enabled by default.
                  **globasciiranges**
                          If set, range expressions used in pattern matching
                          bracket expressions (see **Pattern Matching** above)
                          behave as if in the traditional C locale when
                          performing comparisons.  That is, pattern matching
                          does not take the current locale's collating
                          sequence into account, so **b** will not collate
                          between **A** and **B** , and upper-case and lower-case
                          ASCII characters will collate together.
                  **globskipdots**
                          If set, pathname expansion will never match the
                          filenames _._ and _.._ , even if the pattern begins with
                          a “.”.  This option is enabled by default.
                  **globstar**
                          If set, the pattern ****** used in a pathname expansion
                          context will match all files and zero or more
                          directories and subdirectories.  If the pattern is
                          followed by a **/** , only directories and
                          subdirectories match.
                  **gnu_errfmt**
                          If set, shell error messages are written in the
                          standard GNU error message format.
                  **histappend**
                          If set, the history list is appended to the file
                          named by the value of the **HISTFILE** variable when
                          the shell exits, rather than overwriting the file.
                  **histreedit**
                          If set, and **readline** is being used, the user is
                          given the opportunity to re-edit a failed history
                          substitution.
                  **histverify**
                          If set, and **readline** is being used, the results of
                          history substitution are not immediately passed to
                          the shell parser.  Instead, the resulting line is
                          loaded into the **readline** editing buffer, allowing
                          further modification.
                  **hostcomplete**
                          If set, and **readline** is being used, **bash** will
                          attempt to perform hostname completion when a word
                          containing a **@** is being completed (see **Completing**
                          under **READLINE** above).  This is enabled by default.
                  **huponexit**
                          If set, **bash** will send **SIGHUP** to all jobs when an
                          interactive login shell exits.
                  **inherit_errexit**
                          If set, command substitution inherits the value of
                          the **errexit** option, instead of unsetting it in the
                          subshell environment.  This option is enabled when
                          posix mode is enabled.
                  **interactive_comments**
                          In an interactive shell, a word beginning with **#**
                          causes that word and all remaining characters on
                          that line to be ignored, as in a non-interactive
                          shell (see **COMMENTS** above).  This option is enabled
                          by default.
                  **lastpipe**
                          If set, and job control is not active, the shell
                          runs the last command of a pipeline not executed in
                          the background in the current shell environment.
                  **lithist** If set, and the **cmdhist** option is enabled, multi-
                          line commands are saved to the history with
                          embedded newlines rather than using semicolon
                          separators where possible.
                  **localvar_inherit**
                          If set, local variables inherit the value and
                          attributes of a variable of the same name that
                          exists at a previous scope before any new value is
                          assigned.  The nameref attribute is not inherited.
                  **localvar_unset**
                          If set, calling **unset** on local variables in
                          previous function scopes marks them so subsequent
                          lookups find them unset until that function
                          returns.  This is identical to the behavior of
                          unsetting local variables at the current function
                          scope.
                  **login_shell**
                          The shell sets this option if it is started as a
                          login shell (see **INVOCATION** above).  The value may
                          not be changed.
                  **mailwarn**
                          If set, and a file that **bash** is checking for mail
                          has been accessed since the last time it was
                          checked, **bash** displays the message “The mail in
                          _mailfile_ has been read”.
                  **no_empty_cmd_completion**
                          If set, and **readline** is being used, **bash** does not
                          search **PATH** for possible completions when
                          completion is attempted on an empty line.
                  **nocaseglob**
                          If set, **bash** matches filenames in a
                          case-insensitive fashion when performing pathname
                          expansion (see **Pathname Expansion** above).
                  **nocasematch**
                          If set, **bash** matches patterns in a case-insensitive
                          fashion when performing matching while executing
                          **case** or **[[** conditional commands, when performing
                          pattern substitution word expansions, or when
                          filtering possible completions as part of
                          programmable completion.
                  **noexpand_translation**
                          If set, **bash** encloses the translated results of
                          **$"**...**"** quoting in single quotes instead of double
                          quotes.  If the string is not translated, this has
                          no effect.
                  **nullglob**
                          If set, pathname expansion patterns which match no
                          files (see **Pathname Expansion** above) expand to
                          nothing and are removed, rather than expanding to
                          themselves.
                  **patsub_replacement**
                          If set, **bash** expands occurrences of **& **in the
                          replacement string of pattern substitution to the
                          text matched by the pattern, as described under
                          **Parameter Expansion** above.  This option is enabled
                          by default.
                  **progcomp**
                          If set, enable the programmable completion
                          facilities (see **Programmable Completion** above).
                          This option is enabled by default.
                  **progcomp_alias**
                          If set, and programmable completion is enabled,
                          **bash** treats a command name that doesn't have any
                          completions as a possible alias and attempts alias
                          expansion.  If it has an alias, **bash** attempts
                          programmable completion using the command word
                          resulting from the expanded alias.
                  **promptvars**
                          If set, prompt strings undergo parameter expansion,
                          command substitution, arithmetic expansion, and
                          quote removal after being expanded as described in
                          **PROMPTING** above.  This option is enabled by
                          default.
                  **restricted_shell**
                          The shell sets this option if it is started in
                          restricted mode (see **RESTRICTED SHELL** below).  The
                          value may not be changed.  This is not reset when
                          the startup files are executed, allowing the
                          startup files to discover whether or not a shell is
                          restricted.
                  **shift_verbose**
                          If set, the **shift** builtin prints an error message
                          when the shift count exceeds the number of
                          positional parameters.
                  **sourcepath**
                          If set, the **.**(**source**) builtin uses the value of
                          **PATH** to find the directory containing the file
                          supplied as an argument when the **-p** option is not
                          supplied.  This option is enabled by default.
                  **varredir_close**
                          If set, the shell automatically closes file
                          descriptors assigned using the _{varname}_
                          redirection syntax (see **REDIRECTION** above) instead
                          of leaving them open when the command completes.
                  **xpg_echo**
                          If set, the **echo** builtin expands backslash-escape
                          sequences by default.  If the **posix** shell option is
                          also enabled, **echo** does not interpret any options.
    
           **suspend**[**-f**]
                  Suspend the execution of this shell until it receives a
                  **SIGCONT** signal.  A login shell, or a shell without job
                  control enabled, cannot be suspended; the **-f** option will
                  override this and force the suspension.  The return status
                  is 0 unless the shell is a login shell or job control is
                  not enabled and **-f** is not supplied.
    
           **test** _expr_
           **[**_expr_ **]**
                  Return a status of 0 (true) or 1 (false) depending on the
                  evaluation of the conditional expression _expr_.  Each
                  operator and operand must be a separate argument.
                  Expressions are composed of the primaries described above
                  under **CONDITIONAL EXPRESSIONS**.  **test** does not accept any
                  options, nor does it accept and ignore an argument of **--** as
                  signifying the end of options.
    
                  Expressions may be combined using the following operators,
                  listed in decreasing order of precedence.  The evaluation
                  depends on the number of arguments; see below.  **test** uses
                  operator precedence when there are five or more arguments.
                  **!**_expr_ True if _expr_ is false.
                  **(**_expr_ **)**
                         Returns the value of _expr_.  This may be used to
                         override normal operator precedence.
                  _expr1_ -**a** _expr2_
                         True if both _expr1_ and _expr2_ are true.
                  _expr1_ -**o** _expr2_
                         True if either _expr1_ or _expr2_ is true.
    
                  **test** and **[** evaluate conditional expressions using a set of
                  rules based on the number of arguments.
    
                  0 arguments
                         The expression is false.
                  1 argument
                         The expression is true if and only if the argument
                         is not null.
                  2 arguments
                         If the first argument is **!** , the expression is true
                         if and only if the second argument is null.  If the
                         first argument is one of the unary conditional
                         operators listed above under **CONDITIONAL**
                         **EXPRESSIONS** , the expression is true if the unary
                         test is true.  If the first argument is not a valid
                         unary conditional operator, the expression is false.
                  3 arguments
                         The following conditions are applied in the order
                         listed.  If the second argument is one of the binary
                         conditional operators listed above under **CONDITIONAL**
                         **EXPRESSIONS** , the result of the expression is the
                         result of the binary test using the first and third
                         arguments as operands.  The **-a** and **-o** operators are
                         considered binary operators when there are three
                         arguments.  If the first argument is **!** , the value is
                         the negation of the two-argument test using the
                         second and third arguments.  If the first argument
                         is exactly **(** and the third argument is exactly **)** ,
                         the result is the one-argument test of the second
                         argument.  Otherwise, the expression is false.
                  4 arguments
                         The following conditions are applied in the order
                         listed.  If the first argument is **!** , the result is
                         the negation of the three-argument expression
                         composed of the remaining arguments.  If the first
                         argument is exactly **(** and the fourth argument is
                         exactly **)** , the result is the two-argument test of
                         the second and third arguments.  Otherwise, the
                         expression is parsed and evaluated according to
                         precedence using the rules listed above.
                  5 or more arguments
                         The expression is parsed and evaluated according to
                         precedence using the rules listed above.
    
                  When the shell is in posix mode, or if the expression is
                  part of the **[[** command, the **< **and **> **operators sort using
                  the current locale.  If the shell is not in posix mode, the
                  **test** and **[** commands sort lexicographically using ASCII
                  ordering.
    
                  The historical operator-precedence parsing with 4 or more
                  arguments can lead to ambiguities when it encounters
                  strings that look like primaries.  The POSIX standard has
                  deprecated the **-a** and **-o** primaries and enclosing
                  expressions within parentheses.  Scripts should no longer
                  use them.  It's much more reliable to restrict test
                  invocations to a single primary, and to replace uses of **-a**
                  and **-o** with the shell's **& & **and **||** list operators.
    
           **times** Print the accumulated user and system times for the shell
                  and for processes run from the shell.  The return status is
                  0.
    
           **trap**[**-lpP**] [[_action_] _sigspec_ ...]
                  The _action_ is a command that is read and executed when the
                  shell receives any of the signals _sigspec_.  If _action_ is
                  absent (and there is a single _sigspec_) or **-** , each specified
                  _sigspec_ is reset to the value it had when the shell was
                  started.  If _action_ is the null string the signal specified
                  by each _sigspec_ is ignored by the shell and by the commands
                  it invokes.
    
                  If no arguments are supplied, **trap** displays the actions
                  associated with each trapped signal as a set of **trap**
                  commands that can be reused as shell input to restore the
                  current signal dispositions.  If **-p** is given, and _action_ is
                  not present, then **trap** displays the actions associated with
                  each _sigspec_ or, if none are supplied, for all trapped
                  signals, as a set of **trap** commands that can be reused as
                  shell input to restore the current signal dispositions.
                  The **-P** option behaves similarly, but displays only the
                  actions associated with each _sigspec_ argument.  **-P** requires
                  at least one _sigspec_ argument.  The **-P** or **-p** options may be
                  used in a subshell environment (e.g., command substitution)
                  and, as long as they are used before **trap** is used to change
                  a signal's handling, will display the state of its parent's
                  traps.
    
                  The **-l** option prints a list of signal names and their
                  corresponding numbers.  Each _sigspec_ is either a signal
                  name defined in <_signal.h_ >, or a signal number.  Signal
                  names are case insensitive and the **SIG** prefix is optional.
                  If **-l** is supplied with no _sigspec_ arguments, it prints a
                  list of valid signal names.
    
                  If a _sigspec_ is **EXIT**(0), _action_ is executed on exit from
                  the shell.  If a _sigspec_ is **DEBUG** , _action_ is executed
                  before every _simple command_ , _for_ command, _case_ command,
                  _select_ command, (( arithmetic command, [[ conditional
                  command, arithmetic _for_ command, and before the first
                  command executes in a shell function (see **SHELL GRAMMAR**
                  above).  Refer to the description of the **extdebug** shell
                  option (see **shopt** above) for details of its effect on the
                  **DEBUG** trap.  If a _sigspec_ is **RETURN** , _action_ is executed
                  each time a shell function or a script executed with the **.**
                  or **source** builtins finishes executing.
    
                  If a _sigspec_ is **ERR** , _action_ is executed whenever a pipeline
                  (which may consist of a single simple command), a list, or
                  a compound command returns a non-zero exit status, subject
                  to the following conditions.  The **ERR** trap is not executed
                  if the failed command is part of the command list
                  immediately following a **while** or **until** reserved word, part
                  of the test in an _if_ statement, part of a command executed
                  in a **& & **or **||** list except the command following the final
                  **& & **or **||** , any command in a pipeline but the last (subject
                  to the state of the **pipefail** shell option), or if the
                  command's return value is being inverted using **!**.  These
                  are the same conditions obeyed by the **errexit**(**-e**) option.
    
                  When the shell is not interactive, signals ignored upon
                  entry to the shell cannot be trapped or reset.  Interactive
                  shells permit trapping signals ignored on entry.  Trapped
                  signals that are not being ignored are reset to their
                  original values in a subshell or subshell environment when
                  one is created.  The return status is false if any _sigspec_
                  is invalid; otherwise **trap** returns true.
    
           **true** Does nothing, returns a 0 status.
    
           **type**[**-aftpP**] _name_ [_name_ ...]
                  Indicate how each _name_ would be interpreted if used as a
                  command name.
    
                  If the **-t** option is used, **type** prints a string which is one
                  of _alias_ , _keyword_ , _function_ , _builtin_ , or _file_ if _name_ is an
                  alias, shell reserved word, function, builtin, or
                  executable file, respectively.  If the _name_ is not found,
                  **type** prints nothing and returns a non-zero exit status.
    
                  If the **-p** option is used, **type** either returns the pathname
                  of the executable file that would be found by searching
                  **$PATH** for _name_ or nothing if “type -t name” would not
                  return _file_.  The **-P** option forces a **PATH** search for each
                  _name_ , even if “type -t name” would not return _file_.  If
                  _name_ is present in the table of hashed commands, **-p** and **-P**
                  print the hashed value, which is not necessarily the file
                  that appears first in **PATH**.
    
                  If the **-a** option is used, **type** prints all of the places
                  that contain a command named _name_.  This includes aliases,
                  reserved words, functions, and builtins, but the path
                  search options (**-p** and **-P**) can be supplied to restrict the
                  output to executable files.  **type** does not consult the
                  table of hashed commands when using **-a** with **-p** , and only
                  performs a **PATH** search for _name_.
    
                  The **-f** option suppresses shell function lookup, as with the
                  **command** builtin.  **type** returns true if all of the arguments
                  are found, false if any are not found.
    
           **ulimit**[**-HS**] **-a**
           **ulimit**[**-HS**] [**-bcdefiklmnpqrstuvxPRT**[_limit_]]
                  Provides control over the resources available to the shell
                  and to processes it starts, on systems that allow such
                  control.
    
                  The **-H** and **-S** options specify whether the hard or soft
                  limit is set for the given resource.  A hard limit cannot
                  be increased by a non-root user once it is set; a soft
                  limit may be increased up to the value of the hard limit.
                  If neither **-H** nor **-S** is specified, **ulimit** sets both the
                  soft and hard limits.
    
                  The value of _limit_ can be a number in the unit specified
                  for the resource or one of the special values **hard** , **soft** ,
                  or **unlimited** , which stand for the current hard limit, the
                  current soft limit, and no limit, respectively.  If _limit_
                  is omitted, **ulimit** prints the current value of the soft
                  limit of the resource, unless the **-H** option is given.  When
                  more than one resource is specified, the limit name and
                  unit, if appropriate, are printed before the value.  Other
                  options are interpreted as follows:
                  **-a** Report all current limits; no limits are set.
                  **-b** The maximum socket buffer size.
                  **-c** The maximum size of core files created.
                  **-d** The maximum size of a process's data segment.
                  **-e** The maximum scheduling priority (“nice”).
                  **-f** The maximum size of files written by the shell and
                         its children.
                  **-i** The maximum number of pending signals.
                  **-k** The maximum number of kqueues that may be allocated.
                  **-l** The maximum size that may be locked into memory.
                  **-m** The maximum resident set size (many systems do not
                         honor this limit).
                  **-n** The maximum number of open file descriptors (most
                         systems do not allow this value to be set).
                  **-p** The pipe size in 512-byte blocks (this may not be
                         set).
                  **-q** The maximum number of bytes in POSIX message queues.
                  **-r** The maximum real-time scheduling priority.
                  **-s** The maximum stack size.
                  **-t** The maximum amount of cpu time in seconds.
                  **-u** The maximum number of processes available to a
                         single user.
                  **-v** The maximum amount of virtual memory available to
                         the shell and, on some systems, to its children.
                  **-x** The maximum number of file locks.
                  **-P** The maximum number of pseudoterminals.
                  **-R** The maximum time a real-time process can run before
                         blocking, in microseconds.
                  **-T** The maximum number of threads.
    
                  If _limit_ is supplied, and the **-a** option is not used, _limit_
                  is the new value of the specified resource.  If no option
                  is supplied, then **-f** is assumed.
    
                  Values are in 1024-byte increments, except for **-t** , which is
                  in seconds; **-R** , which is in microseconds; **-p** , which is in
                  units of 512-byte blocks; **-P** , **-T** , **-b** , **-k** , **-n** , and **-u** , which
                  are unscaled values; and, when in posix mode, **-c** and **-f** ,
                  which are in 512-byte increments.  The return status is 0
                  unless an invalid option or argument is supplied, or an
                  error occurs while setting a new limit.
    
           **umask**[**-p**] [**-S**] [_mode_]
                  Set the user file-creation mask to _mode_.  If _mode_ begins
                  with a digit, it is interpreted as an octal number;
                  otherwise it is interpreted as a symbolic mode mask similar
                  to that accepted by chmod(1).  If _mode_ is omitted, **umask**
                  prints the current value of the mask.  The **-S** option
                  without a _mode_ argument prints the mask in a symbolic
                  format; the default output is an octal number.  If the **-p**
                  option is supplied, and _mode_ is omitted, the output is in a
                  form that may be reused as input.  The return status is
                  zero if the mode was successfully changed or if no _mode_
                  argument was supplied, and non-zero otherwise.
    
           **unalias**[-**a**] [_name_ ...]
                  Remove each _name_ from the list of defined aliases.  If **-a**
                  is supplied, remove all alias definitions.  The return
                  value is true unless a supplied _name_ is not a defined
                  alias.
    
           **unset**[-**fv**] [-**n**] [_name_ ...]
                  For each _name_ , remove the corresponding variable or
                  function.  If the **-v** option is given, each _name_ refers to a
                  shell variable, and that variable is removed.  If **-f** is
                  specified, each _name_ refers to a shell function, and the
                  function definition is removed.  If the **-n** option is
                  supplied, and _name_ is a variable with the _nameref_
                  attribute, _name_ will be unset rather than the variable it
                  references.  **-n** has no effect if the **-f** option is supplied.
                  Read-only variables and functions may not be unset.  When
                  variables or functions are removed, they are also removed
                  from the environment passed to subsequent commands.  If no
                  options are supplied, each _name_ refers to a variable; if
                  there is no variable by that name, a function with that
                  name, if any, is unset.  Some shell variables may not be
                  unset.  If any of **BASH_ALIASES** , **BASH_ARGV0** , **BASH_CMDS** ,
                  **BASH_COMMAND** , **BASH_SUBSHELL** , **BASHPID** , **COMP_WORDBREAKS** ,
                  **DIRSTACK** , **EPOCHREALTIME** , **EPOCHSECONDS** , **FUNCNAME** , **GROUPS** ,
                  **HISTCMD** , **LINENO** , **RANDOM** , **SECONDS** , or **SRANDOM** are unset,
                  they lose their special properties, even if they are
                  subsequently reset.  The exit status is true unless a _name_
                  is readonly or may not be unset.
    
           **wait**[**-fn**] [**-p** _varname_] [_id_ ...]
                  Wait for each specified child process _id_ and return the
                  termination status of the last _id_.  Each _id_ may be a
                  process ID _pid_ or a job specification _jobspec_ ; if a jobspec
                  is supplied, **wait** waits for all processes in the job.
    
                  If no options or _id_ s are supplied, **wait** waits for all
                  running background jobs and the last-executed process
                  substitution, if its process id is the same as **$!** , and the
                  return status is zero.
    
                  If the **-n** option is supplied, **wait** waits for any one of the
                  given _id_ s or, if no _id_ s are supplied, any job or process
                  substitution, to complete and returns its exit status.  If
                  none of the supplied _id_ s is a child of the shell, or if no
                  _id_ s are supplied and the shell has no unwaited-for
                  children, the exit status is 127.
    
                  If the **-p** option is supplied, **wait** assigns the process or
                  job identifier of the job for which the exit status is
                  returned to the variable _varname_ named by the option
                  argument.  The variable, which cannot be readonly, will be
                  unset initially, before any assignment.  This is useful
                  only when used with the **-n** option.
    
                  Supplying the **-f** option, when job control is enabled,
                  forces **wait** to wait for each _id_ to terminate before
                  returning its status, instead of returning when it changes
                  status.
    
                  If none of the _id_ s specify one of the shell's active child
                  processes, the return status is 127.  If **wait** is
                  interrupted by a signal, any _varname_ will remain unset, and
                  the return status will be greater than 128, as described
                  under **SIGNALS** above.  Otherwise, the return status is the
                  exit status of the last _id_.
    


## SHELL COMPATIBILITY MODE



           Bash-4.0 introduced the concept of a _shell compatibility level_ ,
           specified as a set of options to the shopt builtin (**compat31** ,
           **compat32** , **compat40** , **compat41** , and so on).  There is only one
           current compatibility level — each option is mutually exclusive.
           The compatibility level is intended to allow users to select
           behavior from previous versions that is incompatible with newer
           versions while they migrate scripts to use current features and
           behavior.  It's intended to be a temporary solution.
    
           This section does not mention behavior that is standard for a
           particular version (e.g., setting **compat32** means that quoting the
           right hand side of the regexp matching operator quotes special
           regexp characters in the word, which is default behavior in
           bash-3.2 and subsequent versions).
    
           If a user enables, say, **compat32** , it may affect the behavior of
           other compatibility levels up to and including the current
           compatibility level.  The idea is that each compatibility level
           controls behavior that changed in that version of **bash** , but that
           behavior may have been present in earlier versions.  For instance,
           the change to use locale-based comparisons with the **[[** command
           came in bash-4.1, and earlier versions used ASCII-based
           comparisons, so enabling **compat32** will enable ASCII-based
           comparisons as well.  That granularity may not be sufficient for
           all uses, and as a result users should employ compatibility levels
           carefully.  Read the documentation for a particular feature to
           find out the current behavior.
    
           Bash-4.3 introduced a new shell variable: **BASH_COMPAT**.  The value
           assigned to this variable (a decimal version number like 4.2, or
           an integer corresponding to the **compat** _NN_ option, like 42)
           determines the compatibility level.
    
           Starting with bash-4.4, **bash** began deprecating older compatibility
           levels.  Eventually, the options will be removed in favor of
           **BASH_COMPAT**.
    
           Bash-5.0 was the final version for which there was an individual
           shopt option for the previous version.  **BASH_COMPAT** is the only
           mechanism to control the compatibility level in versions newer
           than bash-5.0.
    
           The following table describes the behavior changes controlled by
           each compatibility level setting.  The **compat** _NN_ tag is used as
           shorthand for setting the compatibility level to _NN_ using one of
           the following mechanisms.  For versions prior to bash-5.0, the
           compatibility level may be set using the corresponding **compat** _NN_
           shopt option.  For bash-4.3 and later versions, the **BASH_COMPAT**
           variable is preferred, and it is required for bash-5.1 and later
           versions.
    
           **compat31**
                  •      Quoting the rhs of the **[[** command's regexp matching
                         operator (=~) has no special effect.
    
           **compat32**
                  •      The **< **and **> **operators to the **[[** command do not
                         consider the current locale when comparing strings;
                         they use ASCII ordering.
    
           **compat40**
                  •      The **< **and **> **operators to the **[[** command do not
                         consider the current locale when comparing strings;
                         they use ASCII ordering.  **Bash** versions prior to
                         bash-4.1 use ASCII collation and strcmp(3); bash-4.1
                         and later use the current locale's collation
                         sequence and strcoll(3).
    
           **compat41**
                  •      In posix mode, **time** may be followed by options and
                         still be recognized as a reserved word (this is
                         POSIX interpretation 267).
                  •      In _posix_ mode, the parser requires that an even
                         number of single quotes occur in the _word_ portion of
                         a double-quoted parameter expansion and treats them
                         specially, so that characters within the single
                         quotes are considered quoted (this is POSIX
                         interpretation 221).
    
           **compat42**
                  •      The replacement string in double-quoted pattern
                         substitution does not undergo quote removal, as it
                         does in versions after bash-4.2.
                  •      In posix mode, single quotes are considered special
                         when expanding the _word_ portion of a double-quoted
                         parameter expansion and can be used to quote a
                         closing brace or other special character (this is
                         part of POSIX interpretation 221); in later
                         versions, single quotes are not special within
                         double-quoted word expansions.
    
           **compat43**
                  •      Word expansion errors are considered non-fatal
                         errors that cause the current command to fail, even
                         in posix mode (the default behavior is to make them
                         fatal errors that cause the shell to exit).
                  •      When executing a shell function, the loop state
                         (while/until/etc.)  is not reset, so **break** or
                         **continue** in that function will break or continue
                         loops in the calling context.  Bash-4.4 and later
                         reset the loop state to prevent this.
    
           **compat44**
                  •      The shell sets up the values used by **BASH_ARGV** and
                         **BASH_ARGC** so they can expand to the shell's
                         positional parameters even if extended debugging
                         mode is not enabled.
                  •      A subshell inherits loops from its parent context,
                         so **break** or **continue** will cause the subshell to
                         exit.  Bash-5.0 and later reset the loop state to
                         prevent the exit
                  •      Variable assignments preceding builtins like **export**
                         and **readonly** that set attributes continue to affect
                         variables with the same name in the calling
                         environment even if the shell is not in posix mode.
    
           **compat50**
                  •      Bash-5.1 changed the way **$RANDOM** is generated to
                         introduce slightly more randomness.  If the shell
                         compatibility level is set to 50 or lower, it
                         reverts to the method from bash-5.0 and previous
                         versions, so seeding the random number generator by
                         assigning a value to **RANDOM** will produce the same
                         sequence as in bash-5.0.
                  •      If the command hash table is empty, bash versions
                         prior to bash-5.1 printed an informational message
                         to that effect, even when producing output that can
                         be reused as input.  Bash-5.1 suppresses that
                         message when the **-l** option is supplied.
    
           **compat51**
                  •      The **unset** builtin treats attempts to unset array
                         subscripts **@** and ***** differently depending on whether
                         the array is indexed or associative, and differently
                         than in previous versions.
                  •      Arithmetic commands ( **((**...**))**) and the expressions
                         in an arithmetic for statement can be expanded more
                         than once.
                  •      Expressions used as arguments to arithmetic
                         operators in the **[[** conditional command can be
                         expanded more than once.
                  •      The expressions in substring parameter brace
                         expansion can be expanded more than once.
                  •      The expressions in the **$((**...**))** word expansion can
                         be expanded more than once.
                  •      Arithmetic expressions used as indexed array
                         subscripts can be expanded more than once.
                  •      **test -v** , when given an argument of **A[@]** , where **A** is
                         an existing associative array, will return true if
                         the array has any set elements.  Bash-5.2 will look
                         for and report on a key named **@**.
                  •      The ${_parameter_**[:]=**_value_} word expansion will return
                         _value_ , before any variable-specific transformations
                         have been performed (e.g., converting to lowercase).
                         Bash-5.2 will return the final value assigned to the
                         variable.
                  •      Parsing command substitutions will behave as if
                         extended globbing (see the description of the **shopt**
                         builtin above) is enabled, so that parsing a command
                         substitution containing an extglob pattern (say, as
                         part of a shell function) will not fail.  This
                         assumes the intent is to enable extglob before the
                         command is executed and word expansions are
                         performed.  It will fail at word expansion time if
                         extglob hasn't been enabled by the time the command
                         is executed.
    
           **compat52**
                  •      The **test** builtin uses its historical algorithm to
                         parse parenthesized subexpressions when given five
                         or more arguments.
                  •      If the **-p** or **-P** option is supplied to the **bind**
                         builtin, **bind** treats any arguments remaining after
                         option processing as bindable command names, and
                         displays any key sequences bound to those commands,
                         instead of treating the arguments as key sequences
                         to bind.
    


## RESTRICTED SHELL



           If **bash** is started with the name **rbash** , or the **-r** option is
           supplied at invocation, the shell becomes _restricted_.  A
           restricted shell is used to set up an environment more controlled
           than the standard shell.  It behaves identically to **bash** with the
           exception that the following are disallowed or not performed:
    
           •      Changing directories with **cd**.
    
           •      Setting or unsetting the values of **SHELL** , **PATH** , **HISTFILE** ,
                  **ENV** , or **BASH_ENV**.
    
           •      Specifying command names containing **/**.
    
           •      Specifying a filename containing a **/** as an argument to the
                  **.** builtin command.
    
           •      Using the **-p** option to the **.** builtin command to specify a
                  search path.
    
           •      Specifying a filename containing a slash as an argument to
                  the **history** builtin command.
    
           •      Specifying a filename containing a slash as an argument to
                  the **-p** option to the **hash** builtin command.
    
           •      Importing function definitions from the shell environment
                  at startup.
    
           •      Parsing the values of **BASHOPTS** and **SHELLOPTS** from the shell
                  environment at startup.
    
           •      Redirecting output using the >, >|, <>, >&, &>, and >>
                  redirection operators.
    
           •      Using the **exec** builtin command to replace the shell with
                  another command.
    
           •      Adding or deleting builtin commands with the **-f** and **-d**
                  options to the **enable** builtin command.
    
           •      Using the **enable** builtin command to enable disabled shell
                  builtins.
    
           •      Specifying the **-p** option to the **command** builtin command.
    
           •      Turning off restricted mode with **set +r** or **shopt -u**
                  **restricted_shell**.
    
           These restrictions are enforced after any startup files are read.
    
           When a command that is found to be a shell script is executed (see
           **COMMAND EXECUTION** above), **rbash** turns off any restrictions in the
           shell spawned to execute the script.
    


## FILES



           _/bin/bash_
                  The **bash** executable
           _/etc/profile_
                  The systemwide initialization file, executed for login
                  shells
           _~/.bash_profile_
                  The personal initialization file, executed for login shells
           _~/.bashrc_
                  The individual per-interactive-shell startup file
           _~/.bash_logout_
                  The individual login shell cleanup file, executed when a
                  login shell exits
           _~/.bash_history_
                  The default value of **HISTFILE** , the file in which bash saves
                  the command history
           _~/.inputrc_
                  Individual _readline_ initialization file
    


## BUG REPORTS



           If you find a bug in **bash** , you should report it.  But first, you
           should make sure that it really is a bug, and that it appears in
           the latest version of **bash**.  The latest version is always
           available from _ftp://ftp.gnu.org/pub/gnu/bash/_ and
           _http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash- _
           _master.tar.gz_.
    
           Once you have determined that a bug actually exists, use the
           _bashbug_ command to submit a bug report.  If you have a fix, you
           are encouraged to mail that as well!  You may send suggestions and
           “philosophical” bug reports to _bug-bash@gnu.org_ or post them to
           the Usenet newsgroup **gnu.bash.bug**.
    
           ALL bug reports should include:
    
           The version number of **bash**
           The hardware and operating system
           The compiler used to compile
           A description of the bug behavior
           A short script or “recipe” which exercises the bug
    
           _bashbug_ inserts the first three items automatically into the
           template it provides for filing a bug report.
    
           Comments and bug reports concerning this manual page should be
           directed to _chet.ramey@case.edu_.
    


## BUGS



           It's too big and too slow.
    
           There are some subtle differences between **bash** and traditional
           versions of **sh** , mostly because of the POSIX specification.
    
           Aliases are confusing in some uses.
    
           Shell builtin commands and functions are not
           stoppable/restartable.
    
           Compound commands and command lists of the form “a ; b ; c” are
           not handled gracefully when combined with process suspension.
           When a process is stopped, the shell immediately executes the next
           command in the list or breaks out of any existing loops.  It
           suffices to enclose the command in parentheses to force it into a
           subshell, which may be stopped as a unit, or to start the command
           in the background and immediately bring it into the foreground.
    
           Array variables may not (yet) be exported.
    


* * *