Built-in Shell Variables (Learning the Korn Shell, 2nd Edition)

B.4. Built-in Shell Variables

Here is a summary of all built-in shell variables:

Variable	Chapter	Meaning
`#`	4	Number of arguments given to current process.
`@`	4	Command-line arguments to current process. Inside double quotes, expands to individual arguments.
`*`	4	Command-line arguments to current process. Inside double quotes, expands to a single argument.
`-` (hyphen)		Options given to shell on invocation.
`?`	5	Exit status of previous command.
`$`	8	Process ID of shell process.
`_` (underscore)	3	Inside `$MAILPATH`: the filename that triggered a "you have mail" message. On the command line: last argument to previous command. Inside a script: the full pathname used to find and run the script.
`!`	8	Process ID of last background command.
`.sh.edchar`	10	Characters entered when processing a KEYBD trap.
`.sh.edcol`	10	Position of the cursor in the most recent KEYBD trap.
`.sh.edmode`	10	Equal to ESC in vi-mode, empty otherwise.
`.sh.edtext`	10	Characters in the input buffer during a KEYBD trap.
`.sh.match`	4	Array variable with text that matched pattern in variable substitution. (Starting with ksh93l.)
`.sh.name`	9	Name of a variable executing a discipline function.
`.sh.subscript`	9	Subscript of an array variable executing a discipline function.
`.sh.value`	9	Value of the variable executing a discipline function.
`.sh.version`	4, 9	Version of ksh.
`CDPATH`	3	List of directories for cd command to search.
`COLUMNS`	3	Width of display in columns (for editing modes and `select`).
`EDITOR`	2	Used to set editing mode; also used by mail and other programs. Overriden by `VISUAL`, if that is set.
`ENV`	3	Name of file to run as environment file when shell is invoked.
`FCEDIT`	2	Obsolete default editor for hist command.
`FIGNORE`	1	Pattern for files to ignore during pattern expansion.
`FPATH`	4	Search path for autoloaded functions.
`HISTCMD`	2	Number of current command in command history.
`HISTEDIT`	2	Default editor for hist command.
`HISTFILE`	2	Name of command history file.
`HISTSIZE`	2	Number of lines kept in history file.
`HOME`	3	Home (login) directory.
`IFS`	7	Internal field separator: list of characters that act as word separators. Normally set to space, TAB, and newline.
`LANG`		Default name of current locale; overridden by the other `LC_*` variables.
`LC_ALL`		Name of current locale; overrides `LANG` and the other `LC_*` variables.
`LC_COLLATE`		Name of current locale for character collation (sorting) purposes.
`LC_CTYPE`		Name of current locale for character class determination during pattern matching; see Chapter 4.
`LC_NUMERIC`		Name of current locale for number formatting (decimal point, thousands separator).
`LINENO`	9	Number of line in script or function that just ran.
`LINES`	3	Height of display in lines (for `select` command).
`MAIL`	3	Name of file to check for new mail.
`MAILCHECK`	3	How often (in seconds) to check for new mail.
`MAILPATH`	3	List of file names to check for new mail, if `MAIL` is not set.
`OLDPWD`	3	Previous working directory.
`OPTARG`	6	Argument to option being processed by getopts.
`OPTIND`	6	Number of first argument after options.
`PATH`	3	Search path for commands.
`PPID`	8	Process ID of parent process.
`PS1`	3	Primary command prompt string.
`PS2`	3	Prompt string for line continuations.
`PS3`	5	Prompt string for `select` command.
`PS4`	9	Prompt string for xtrace option.
`PWD`	3	Current working directory.
`RANDOM`	9	Random number between 0 and 32767 (2¹⁵-1).
`REPLY`	5, 7	User's response to `select` command; result of read command if no variable names given.
`SECONDS`	3	Number of seconds since shell was invoked.
`SHELL`	3	Full pathname of shell programs should use to run commands.
`TMOUT`	5, 7, 10	If set to a positive integer, number of seconds between commands after which shell automatically terminates. Also applies to reading responses to `select` and read.
`VISUAL`	2	Used to set editing mode.


B.3. Predefined Aliases		B.5. Test Operators