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 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 (215-1). |
| 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 `!#'. |
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