Environment Variables

B.3 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.
	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 to search.
DIRSTACK	4,6	ARU	The current contents of the directory stack.
EUID		R	The effective user ID of the current user .
FCEDIT	2		The default editor for fc command.
FIGNORE		L	A list of names to ignore when doing filename completion.
GLOBIGNORE		L	A list of patterns defining filenames to ignore during pathname expansion.
GROUPS		AR	An array containing a list of groups of which the current user is a member.
IFS	7		The Internal Field Separator: a list of characters that act as word separators. Normally set to SPACE, TAB, and NEWLINE.
HISTCMD	3	U	The history number of the current command.
HISTCONTROL	3		Controls what is entered in the command history.
HISTFILE	2		The name of the command history file.
HISTIGNORE	3		A list of patterns to decide what should be retained in the history list.
HISTSIZE	2		The number of lines kept in the command history.
HISTFILESIZE	3		The maximum number of lines kept in the history file.
HOME	3		The home (login) directory.
HOSTFILE	3		The file to be used for hostname completion.
HOSTNAME			The name of the current host.
HOSTTYPE	3		The type of machine bash is running on.
IGNOREEOF	3		The number of EOF characters received before exiting an interactive shell.
INPUTRC	2		The readline startup file.
LANG			Used to determine the locale category for any category not specifically selected with a variable starting with LC_ .
LC_ALL			Overrides the value of LANG and any other LC_ variable specifying a locale category.
LC_COLLATE			Determines the collation order used when sorting the results of pathname expansion.
LC_MESSAGES			This variable determines the locale used to translate double-quoted strings preceded by a $ .
LINENO	9	U	The number of the line that just ran in a script or function.
MACHTYPE			A string describing the system on which bash is executing.
MAIL	3		The name of the file to check for new mail.
MAILCHECK	3		How often (in seconds) to check for new mail.
MAILPATH	3	L	A list of file names to check for new mail, if MAIL is not set.
OLDPWD	3		The previous working directory.
OPTARG	6		The value of the last option argument processed by getopts .
OPTERR	6		If set to 1, display error messages from getopts .
OPTIND	6		The number of the first argument after options.
OSTYPE			The operating system on which bash is executing.
PATH	3	L	The search path for commands.
PIPESTATUS	6	A	An array variable containing a list of exit status values from the processes in the most recently executed foreground pipeline.
PROMPT_COMMAND			The value is executed as a command before the primary prompt is issued.
PS1	3		The primary command prompt string.
PS2	3		The prompt string for line continuations.
PS3	5		The prompt string for the select command.
PS4	9		The prompt string for the xtrace option.
PPID	8	R	The process ID of the parent process.
PWD	3		The current working directory.
RANDOM	9	U	A random number between 0 and 32767 (2 15 -1).
REPLY	5, 7		The user's response to the select command; result of the read command if no variable names are given.
SECONDS	3	U	The number of seconds since the shell was invoked.
SHELL	3		The full pathname of the shell.
SHELLOPTS		LR	A list of enabled shell options.
SHLVL			Incremented by one each time an instance of bash is invoked.
TIMEFORMAT			Specifies the format for the output from using the time reserved word on a command pipeline.
TMOUT	10		If set to a positive integer, the number of seconds after which the shell automatically terminates if no input is received.
UID		R	The user ID of the current user.
auto_resume			Controls how job control works.
histchars			Specifies what to use as the history control characters. Normally set to the string `!#'.