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Learning the bash Shell, Second Edition by Bill Rosenblatt, Cameron Newham

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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
* 4R

The positional parameters given to the current script or function.

@ 4R

The positional parameters given to the current script or function.

# 4R

The number of arguments given to the current script or function.

-  R

Options given to the shell on invocation.

? 5R

Exit status of the previous command.

 R

Last argument to the previous command.

$ 8R

Process ID of the shell process.

! 8R

Process ID of the last background command.

0 4R

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 3,6AR

Version information for this instance of bash. Each element of the array holds parts of the version number.

CDPATH 3L

A list of directories for the cd command ...

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