Learning the bash Shell, Second Edition

Environment Variables

Table 2.4 shows a complete list of environment variables available in bash 2.0. 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 BASH_VERSINFO, DIRSTACK, GLOBIGNORE, GROUPS, HISTIGNORE, HOSTNAME, 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 B-4. Environment Variables

Variable	Chapter	Type	Description
*	4	R	The positional parameters given to the current script or function.
@	4	R	The positional parameters given to the current script or function.
#	4	R	The number of arguments given to the current script or function.
-		R	Options given to the shell on invocation.
?	5	R	Exit status of the previous command.
		R	Last argument to the previous command.
$	8	R	Process ID of the shell process.
!	8	R	Process ID of the last background command.
0	4	R	Name of the shell or shell script.
BASH	3		The full pathname used to invoke this instance of bash.
BASH_ENV	3		The name of a file to run as the environment file when the shell is invoked.
BASH_VERSION	3		The version number of this instance of bash.
BASH_VERSINFO	3,6	AR	Version information for this instance of bash. Each element of the array holds parts of the version number.
CDPATH	3	L	A list of directories for the cd command ...