bash Cookbook

Built-in Shell Variables

Table A-5 shows a complete list of environment variables available in bash 3.0. The letters in the Type column of the table have the following meanings: A = Array, L = colon-separated list, R = read-only, U = unsetting it causes it to lose its special meaning.

Note that the variables beginning BASH_ and beginning COMP, as well as the variables DIRSTACK, FUNCNAME, GLOBIGNORE, GROUPS, HISTIGNORE, HOSTNAME, HISTTIMEFORMAT, LANG, LC_ALL, LC_COLLATE, LC_MESSAGE, MACHTYPE, PIPESTATUS, SHELLOPTS, and TIMEFORMAT are not available in versions prior to 2.0. BASH_ENV replaces ENV found in earlier versions.

Table A-5. Built-in shell environment variables

Variable	Type	Description
*	R	A single string containing the positional parameters given to the current script or function, separated by the first character of $IFS (e.g., arg1 arg2 arg3).
@	R	Each of the positional parameters given to the current script or function, given as a list of double-quoted strings (e.g., "arg1" "arg2" "arg3").
#	R	The number of arguments given to the current script or function.
-	R	Options given to the shell on invocation.
?	R	Exit status of the previous command.
_	R	Last argument to the previous command.
$	R	Process ID of the shell process.
!	R	Process ID of the last background command.
0	R	Name of the shell or shell script.
BASH		The full pathname used to invoke this instance of bash.
BASH_ARGC	A	An array of values, which are the number of parameters in each frame of the current bash execution call stack. The number of ...