# xargs

## NAME



           xargs - build and execute command lines from standard input
    


## SYNOPSIS



           **xargs**[_options_] [_command_ [_initial-arguments_]]
    


## DESCRIPTION



           This manual page documents the GNU version of **xargs**.  **xargs** reads
           items from the standard input, delimited by blanks (which can be
           protected with double or single quotes or a backslash) or new‐
           lines, and executes the _command_ (default is _echo_) one or more
           times with any _initial-arguments_ followed by items read from stan‐
           dard input.  Blank lines on the standard input are ignored.
    
           The command line for _command_ is built up until it reaches a sys‐
           tem-defined limit (unless the **-n** and **-L** options are used).  The
           specified _command_ will be invoked as many times as necessary to
           use up the list of input items.  In general, there will be many
           fewer invocations of _command_ than there were items in the input.
           This will normally have significant performance benefits.  Some
           commands can usefully be executed in parallel too; see the **-P** op‐
           tion.
    
           Because Unix filenames can contain blanks and newlines, this de‐
           fault behaviour is often problematic; filenames containing blanks
           and/or newlines are incorrectly processed by **xargs**.  In these sit‐
           uations it is better to use the **-0** option, which prevents such
           problems.  When using this option you will need to ensure that the
           program which produces the input for **xargs** also uses a null char‐
           acter as a separator.  If that program is GNU **find** for example,
           the **-print0** option does this for you.
    
           If any invocation of the command exits with a status of 255, **xargs**
           will stop immediately without reading any further input.  An error
           message is issued on stderr when this happens.
    


## OPTIONS



           **-0, --null**
                  Input items are terminated by a null character instead of
                  by whitespace, and the quotes and backslash are not special
                  (every character is taken literally).  Disables the end-of-
                  file string, which is treated like any other argument.
                  Useful when input items might contain white space, quote
                  marks, or backslashes.  The GNU find (and from Issue 8,
                  POSIX) -print0 option produces input suitable for this
                  mode.
    
           **-a** _file_**, --arg-file=**_file_
                  Read items from _file_ instead of standard input.  If you use
                  this option, stdin remains unchanged when commands are run.
                  Otherwise, stdin is redirected from _/dev/null_.
    
           **--delimiter=**_delim_**, -d** _delim_
                  Input items are terminated by the specified character.  The
                  specified delimiter may be a single character, a C-style
                  character escape such as **\n** , or an octal or hexadecimal es‐
                  cape code.  Octal and hexadecimal escape codes are under‐
                  stood as for the **printf** command.  Multibyte characters are
                  not supported.  When processing the input, quotes and back‐
                  slash are not special; every character in the input is tak‐
                  en literally.  The **-d** option disables any end-of-file
                  string, which is treated like any other argument.  You can
                  use this option when the input consists of simply newline-
                  separated items, although it is almost always better to de‐
                  sign your program to use **--null** where this is possible.
    
           **-E** _eof-str_
                  Set the end-of-file string to _eof-str_.  If the end-of-file
                  string occurs as a line of input, the rest of the input is
                  ignored.  If neither **-E** nor **-e** is used, no end-of-file
                  string is used.
    
           **-e**[_eof-str_], **--eof**[_=eof-str_]
                  This option is a synonym for the **-E** option.  Use **-E** in‐
                  stead, because it is POSIX compliant while this option is
                  not.  If _eof-str_ is omitted, there is no end-of-file
                  string.  If neither **-E** nor **-e** is used, no end-of-file
                  string is used.
    
           **-I** _replace-str_
                  Replace occurrences of _replace-str_ in the initial-arguments
                  with names read from standard input.  Also, unquoted blanks
                  do not terminate input items; instead the separator is the
                  newline character.  Implies **-x** and **-L** 1.
    
           **-i**[_replace-str_], **--replace**[_=replace-str_]
                  This option is a synonym for **-I** _replace-str_ if _replace-str_
                  is specified.  If the _replace-str_ argument is missing, the
                  effect is the same as **-I**{}.  The **-i** option is deprecated;
                  use **-I** instead.
    
           **-L** _max-lines_
                  Use at most _max-lines_ nonblank input lines per command
                  line.  Trailing blanks cause an input line to be logically
                  continued on the next input line.  Implies **-x**.
    
           **-l**[_max-lines_], **--max-lines**[=_max-lines_]
                  Synonym for the **-L** option.  Unlike **-L** , the _max-lines_ argu‐
                  ment is optional.  If _max-lines_ is not specified, it de‐
                  faults to one.  The **-l** option is deprecated since the POSIX
                  standard specifies **-L** instead.
    
           **-n** _max-args_ , **--max-args** =_max-args_
                  Use at most _max-args_ arguments per command line.  Fewer
                  than _max-args_ arguments will be used if the size (see the
                  **-s** option) is exceeded, unless the **-x** option is given, in
                  which case **xargs** will exit.
    
           **-P** _max-procs_ , **--max-procs** =_max-procs_
                  Run up to _max-procs_ processes at a time; the default is 1.
                  If _max-procs_ is 0, **xargs** will run as many processes as pos‐
                  sible at a time.  Use the **-n** option or the **-L** option with
                  **-P** ; otherwise chances are that only one exec will be done.
                  While **xargs** is running, you can send its process a SIGUSR1
                  signal to increase the number of commands to run simultane‐
                  ously, or a SIGUSR2 to decrease the number.  You cannot in‐
                  crease it above an implementation-defined limit (which is
                  shown with --show-limits).  You cannot decrease it below 1.
                  **xargs** never terminates its commands; when asked to de‐
                  crease, it merely waits for more than one existing command
                  to terminate before starting another.  **xargs** always waits
                  for all child processes to exit before exiting itself (but
                  see BUGS).
    
                  If you do not use the **-P** option, **xargs** will not handle the
                  SIGUSR1 and SIGUSR2 signals, meaning that they will termi‐
                  nate the program (unless they were blocked in the parent
                  process before **xargs** was started).
    
                  **Please note** that it is up to the called processes to prop‐
                  erly manage parallel access to shared resources.  For exam‐
                  ple, if more than one of them tries to print to stdout, the
                  output will be produced in an indeterminate order (and very
                  likely mixed up) unless the processes collaborate in some
                  way to prevent this.  Using some kind of locking scheme is
                  one way to prevent such problems.  In general, using a
                  locking scheme will help ensure correct output but reduce
                  performance.  If you don't want to tolerate the performance
                  difference, simply arrange for each process to produce a
                  separate output file (or otherwise use separate resources).
    
           **-o, --open-tty**
                  Reopen stdin as _/dev/tty_ in the child process before exe‐
                  cuting the command.  This is useful if you want **xargs** to
                  run an interactive application.
    
           **-p, --interactive**
                  Prompt the user about whether to run each command line and
                  read a line from the terminal.  Only run the command line
                  if the response starts with `y' or `Y'.  Implies **-t**.
    
           **--process-slot-var** =_name_
                  Set the environment variable _name_ to a unique value in each
                  running child process.  Values are reused once child
                  processes exit.  This can be used in a rudimentary load
                  distribution scheme, for example.
    
           **-r, --no-run-if-empty**
                  If the standard input does not contain any nonblanks, do
                  not run the command.  Normally, the command is run once
                  even if there is no input.  This option is a GNU extension.
    
           **-s** _max-chars_ , **--max-chars** _=max-chars_
                  Use at most _max-chars_ characters per command line, includ‐
                  ing the command and initial-arguments and the terminating
                  nulls at the ends of the argument strings.  The largest al‐
                  lowed value is system-dependent, and is calculated as the
                  argument length limit for exec, less the size of your envi‐
                  ronment, less 2048 bytes of headroom.  If this value is
                  more than 128 KiB, 128 KiB is used as the default value;
                  otherwise, the default value is the maximum.  1 KiB is 1024
                  bytes.  **xargs** automatically adapts to tighter constraints.
    
           **--show-limits**
                  Display the limits on the command-line length which are im‐
                  posed by the operating system, **xargs** ' choice of buffer size
                  and the **-s** option.  Pipe the input from _/dev/null_ (and per‐
                  haps specify **--no-run-if-empty**) if you don't want **xargs** to
                  do anything.
    
           **-t, --verbose**
                  Print the command line on the standard error output before
                  executing it.
    
           **-x, --exit**
                  Exit if the size (see the **-s** option) is exceeded.
    
           **--** Delimit the option list.  Later arguments, if any, are
                  treated as operands even if they begin with _-_.  For exam‐
                  ple, **xargs -- --help** runs the command _--help_ (found in
                  _PATH_) instead of printing the usage text, and **xargs --**
                  **--mycommand** runs the command _--mycommand_ instead of reject‐
                  ing this as unrecognized option.
    
           **--help** Print a summary of the options to **xargs** and exit.
    
           **--version**
                  Print the version number of **xargs** and exit.
    
           The options **--max-lines**(**-L** , **-l**), **--replace**(**-I** , **-i**) and **--max-**
           **args**(**-n**) are mutually exclusive.  If some of them are specified
           at the same time, then **xargs** will generally use the option speci‐
           fied last on the command line, i.e., it will reset the value of
           the offending option (given before) to its default value.  Addi‐
           tionally, **xargs** will issue a warning diagnostic on _stderr_.  The
           exception to this rule is that the special _max-args_ value _1_
           ('**-n** _1_ ') is ignored after the **--replace** option and its aliases **-I**
           and **-i** , because it would not actually conflict.
    


## EXAMPLES



           **find /tmp -name core -type f -print | xargs /bin/rm -f**
    
           Find files named **core** in or below the directory **/tmp** and delete
           them.  Note that this will work incorrectly if there are any file‐
           names containing newlines or spaces.
    
           **find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f**
    
           Find files named **core** in or below the directory **/tmp** and delete
           them, processing filenames in such a way that file or directory
           names containing spaces or newlines are correctly handled.
    
           **find /tmp -depth -name core -type f -delete**
    
           Find files named **core** in or below the directory **/tmp** and delete
           them, but more efficiently than in the previous example (because
           we avoid the need to use fork(2) and **exec**(2) to launch **rm** and we
           don't need the extra **xargs** process).
    
           **cut -d: -f1 < /etc/passwd | sort | xargs echo**
    
           Generates a compact listing of all the users on the system.
    


## EXIT STATUS



           **xargs** exits with the following status:
    
                  0      if it succeeds
    
                  123    if any invocation of the command exited with status
                         1–125
    
                  124    if the command exited with status 255
    
                  125    if the command is killed by a signal
    
                  126    if the command cannot be run
    
                  127    if the command is not found
    
                  1      if some other error occurred.
    
           Exit codes greater than 128 are used by the shell to indicate that
           a program died due to a fatal signal.
    


## STANDARDS CONFORMANCE



           The long-standing **-0** option of **xargs** will be included in Issue 8
           of the POSIX standard.
    
           As of GNU xargs version 4.2.9, the default behaviour of **xargs** is
           not to have a logical end-of-file marker.  POSIX (IEEE Std 1003.1,
           2004 Edition) allows this.
    
           The -l and -i options appear in the 1997 version of the POSIX
           standard, but do not appear in the 2004 version of the standard.
           Therefore you should use -L and -I instead, respectively.
    
           The -o option is an extension to the POSIX standard for better
           compatibility with BSD.
    
           The POSIX standard allows implementations to have a limit on the
           size of arguments to the **exec** functions.  This limit could be as
           low as 4096 bytes including the size of the environment.  For
           scripts to be portable, they must not rely on a larger value.
           However, I know of no implementation whose actual limit is that
           small.  The **--show-limits** option can be used to discover the actu‐
           al limits in force on the current system.
    
           In versions of **xargs** up to and including version 4.9.0, SIGUSR1
           and SIGUSR2 would not cause **xargs** to terminate even if the **-P** op‐
           tion was not used.
    


## BUGS



           It is not possible for **xargs** to be used securely, since there will
           always be a time gap between the production of the list of input
           files and their use in the commands that **xargs** issues.  If other
           users have access to the system, they can manipulate the filesys‐
           tem during this time window to force the action of the commands
           **xargs** runs to apply to files that you didn't intend.  For a more
           detailed discussion of this and related problems, please refer to
           the ``Security Considerations'' chapter in the findutils Texinfo
           documentation.  The **-execdir** option of **find** can often be used as a
           more secure alternative.
    
           When you use the **-I** option, each line read from the input is
           buffered internally.  This means that there is an upper limit on
           the length of input line that **xargs** will accept when used with the
           **-I** option.  To work around this limitation, you can use the **-s** op‐
           tion to increase the amount of buffer space that **xargs** uses, and
           you can also use an extra invocation of **xargs** to ensure that very
           long lines do not occur.  For example:
    
           **somecommand | xargs -s 50000 echo | xargs -I '{}' -s 100000 rm**
           **'{}'**
    
           Here, the first invocation of **xargs** has no input line length limit
           because it doesn't use the **-i** option.  The second invocation of
           **xargs** does have such a limit, but we have ensured that it never
           encounters a line which is longer than it can handle.  This is not
           an ideal solution.  Instead, the **-i** option should not impose a
           line length limit, which is why this discussion appears in the
           BUGS section.  The problem doesn't occur with the output of
           find(1) because it emits just one filename per line.
    
           In versions of **xargs** up to and including version 4.9.0, **xargs -P**
           would exit while some of its children were still running, if one
           of them exited with status 255.
    


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