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| Appendix B Reference Lists |

## B.3 Built-in Shell Variables

Variable | Chapter | Meaning
--- | --- | ---
# | 4 | Number of arguments given to current process.
- |  | Options given to shell on invocation.
? | 5 | Exit status of previous command.
$ | 8 | Process ID of shell process.
_ |  | Last argument to previous command.
! | 8 | Process ID of last background command.
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.
ERRNO | A | Error number of last system call that failed.
ENV | 3 | Name of file to run as environment file when shell is invoked.
FCEDIT | 2 | Default editor for fc command.
FPATH | 4 | Search path for autoloaded functions.
IFS | 7 | Internal field separator: list of characters that act as word separators. Normally set to SPACE, TAB, and NEWLINE.
HISTFILE | 2 | Name of command history file.
HISTSIZE | 2 | Number of lines kept in history file.
HOME | 3 | Home (login) directory.
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.
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.
PPID | 8 | Process ID of parent process.
PWD | 3 | Current working directory.
RANDOM | 9 | Random number between 0 and 32767 (2215-1).
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.
TMOUT | 10 | If set to a positive integer, number of seconds between commands after which shell automatically terminates.
VISUAL | 2 | Used to set editing mode.

B.2 Built-in Commands and Keywords |  | B.4 Test Operators