Mac OS X Tiger in a Nutshell

Built-in Shell Variables

Built-in variables are set automatically by the shell and are typically used inside shell scripts. Built-in variables can use the variable substitution patterns shown earlier. When setting variables, you don’t include dollar signs, but when referencing their values later, the dollar signs are necessary.

Tables 5-26 through Table 5-29 show the commonly used built-in variables in bash.

Table 5-26. Behavior-altering variables

Variable	Meaning
auto_resume	Allows a background job to be brought to the foreground simply by entering a substring of the job’s command line. Values can be substring (resume if the user’s string matches part of the command), exact (string must exactly match command), or another value (string must match at beginning of command).
BASH_ENV	Startup file of commands to execute, if bash is invoked to run a script.
CDPATH	Colon-separated list of directories to search for the directory passed in a cd command.
EDITOR	Pathname of your preferred text editor.
IFS	Word separator; used by shell to parse commands into their elements. The default separators are space, tab, and newline.
IGNOREEOF	If nonzero, don’t allow use of a single Ctrl-D (the end-of-file or EOF character) to log off; use the exit command to log off.
PATH	Colon-separated list of directories to search for each command.
PROMPT_COMMAND	Command that bash executes before issuing a prompt for a new command.
PS1	Prompt displayed before each new command; ...