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 are ignored.  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 processes in the most-recently-executed foreground pipeline (which may contain only a single command). 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.  If RANDOM is unset, it loses its special properties, even if it is subsequently reset. 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, the number of seconds since shell invocation is returned.  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 is always determined by querying the system clock.  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, each shell option in the list will be enabled before reading any startup files.  This variable is read-only. SHLVL  Incremented by one each time an instance of bash is started. SRANDOM This variable expands to a 32-bit pseudo-random number each time it is referenced. The random number generator is not linear on systems that support /dev/urandom or arc4random, 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.