Variables used by the Bourne shell

The shell uses the following variables. Although the shell sets some of them, you can set or reset all of them.

Item	Description
`CDPATH`	Specifies the search path for the cd (change directory) command.
`HOME`	Indicates the name of your login directory, which is the directory that becomes the current directory upon completion of a login. The login program initializes this variable. The cd command uses the value of the `$HOME` variable as its default value. Using this variable rather than an explicit path name in a shell procedure allows the procedure to be run from a different directory without alterations.
`IFS`	The characters that are IFS (internal field separators), which are the characters that the shell uses during blank interpretation. The shell initially sets the `IFS` variable to include the blank, tab, and newline characters.
`LANG`	Determines the locale to use for the locale categories when both the `LC_ALL` variable and the corresponding environment variable (beginning with `LC_`) do not specify a locale.
`LC_ALL`	Determines the locale to be used to override any values for locale categories specified by the settings of the `LANG` environment variable or any environment variables beginning with `LC_`.
`LC_COLLATE`	Defines the collating sequence to use when sorting names and when character ranges occur in patterns.
`LC_CTYPE`	Determines the locale for the interpretation of sequences of bytes of text data as characters (that is, single versus multibyte characters in arguments and input files), which characters are defined as letters (alpha character class), and the behavior of character classes within pattern matching.
`LC_MESSAGES`	Determines the language in which messages should be written.
`LIBPATH`	Specifies the search path for shared libraries.
`LOGNAME`	Specifies your login name, marked `readonly` in the /etc/profile file.
`MAIL`	Indicates the path name of the file used by the mail system to detect the arrival of new mail. If this variable is set, the shell periodically checks the modification time of this file and displays the value of `$MAILMSG` if the time changes and the length of the file is greater than 0. Set the `MAIL` variable in the .profile file. The value normally assigned to it by users of the mail command is /usr/spool/mail/$LOGNAME.
`MAILCHECK`	The number of seconds that the shell lets elapse before checking again for the arrival of mail in the files specified by the `MAILPATH` or `MAIL` variables. The default value is 600 seconds (10 minutes). If you set the `MAILCHECK` variable to 0, the shell checks before each prompt.
`MAILMSG`	The mail notification message. If you explicitly set the `MAILMSG` variable to a null string (`MAILMSG=""`), no message is displayed.
`MAILPATH`	A list of file names separated by colons. If this variable is set, the shell informs you of the arrival of mail in any of the files specified in the list. You can follow each file name by a `%` and a message to be displayed when mail arrives. Otherwise, the shell uses the value of the `MAILMSG` variable or, by default, the message `[YOU HAVE NEW MAIL]`. Note: When the `MAILPATH` variable is set, these files are checked instead of the file set by the `MAIL` variable. To check the files set by the `MAILPATH` variable and the file set by the `MAIL` variable, specify the MAIL file in your list of MAILPATH files.
`PATH`	The search path for commands, which is an ordered list of directory path names separated by colons. The shell searches these directories in the specified order when it looks for commands. A null string anywhere in the list represents the current directory. The `PATH` variable is normally initialized in the /etc/environment file, usually to /usr/bin:/etc:/usr/sbin:/usr/ucb:/usr/bin/X11:/sbin. You can reset this variable to suit your own needs. The `PATH` variable provided in your .profile file also includes $HOME/bin and your current directory. If you have a project-specific directory of commands, for example, /project/bin, that you want searched before the standard system directories, set your `PATH` variable as follows: `PATH=/project/bin:$PATH` The best place to set your `PATH` variable to a value other than the default value is in your $HOME/.profile file. You cannot reset the `PATH` variable if you are executing commands under the restricted shell.
`PS1`	The string to be used as the primary system prompt. An interactive shell displays this prompt string when it expects input. The default value of the `PS1` variable is `$` followed by a blank space for nonroot users.
`PS2`	The value of the secondary prompt string. If the shell expects more input when it encounters a newline character in its input, it prompts with the value of the `PS2` variable. The default value of the `PS2` variable is `>` followed by a blank space.
`SHACCT`	The name of a file that you own. If this variable is set, the shell writes an accounting record in the file for each shell script executed. You can use accounting programs such as acctcom and acctcms to analyze the data collected.
`SHELL`	The path name of the shell, which is kept in the environment. This variable should be set and exported by the $HOME/.profile file of each restricted login.
`TIMEOUT`	The number of minutes a shell remains inactive before it exits. If this variable is set to a value greater than zero (0), the shell exits if a command is not entered within the prescribed number of seconds after issuing the `PS1` prompt. (Note that the shell can be compiled with a maximum boundary that cannot be exceeded for this value.) A value of zero indicates no time limit.