Common shell variable names and usage.
BASH_VERSION
[tab]Version information for this Bash.
CDPATH
[tab]A colon-separated list of directories to search
[tab][tab]for directories given as arguments to `cd'.
GLOBIGNORE
[tab]A colon-separated list of patterns describing filenames to
[tab][tab]be ignored by pathname expansion.
HISTFILE
[tab]The name of the file where your command history is stored.
HISTFILESIZE
[tab]The maximum number of lines this file can contain.
HISTSIZE
[tab]The maximum number of history lines that a running
[tab][tab]shell can access.
HOME
[tab]The complete pathname to your login directory.
HOSTNAME
[tab]The name of the current host.
HOSTTYPE
[tab]The type of CPU this version of Bash is running under.
IGNOREEOF
[tab]Controls the action of the shell on receipt of an EOF
[tab][tab]character as the sole input. If set, then the value
[tab][tab]of it is the number of EOF characters that can be seen
[tab][tab]in a row on an empty line before the shell will exit
[tab][tab](default 10). When unset, EOF signifies the end of input.
MACHTYPE
[tab]A string describing the current system Bash is running on.
MAILCHECK
[tab]How often, in seconds, Bash checks for new mail.
MAILPATH
[tab]A colon-separated list of filenames which Bash checks
[tab][tab]for new mail.
OSTYPE
[tab]The version of Unix this version of Bash is running on.
PATH
[tab]A colon-separated list of directories to search when
[tab][tab]looking for commands.
PROMPT_COMMAND
[tab]A command to be executed before the printing of each
[tab][tab]primary prompt.
PS1
[tab][tab]The primary prompt string.
PS2
[tab][tab]The secondary prompt string.
PWD
[tab][tab]The full pathname of the current directory.
SHELLOPTS
[tab]A colon-separated list of enabled shell options.
TERM
[tab]The name of the current terminal type.
TIMEFORMAT
[tab]The output format for timing statistics displayed by the
[tab][tab]`time' reserved word.
auto_resume
[tab]Non-null means a command word appearing on a line by
[tab][tab]itself is first looked for in the list of currently
[tab][tab]stopped jobs. If found there, that job is foregrounded.
[tab][tab]A value of `exact' means that the command word must
[tab][tab]exactly match a command in the list of stopped jobs. A
[tab][tab]value of `substring' means that the command word must
[tab][tab]match a substring of the job. Any other value means that
[tab][tab]the command must be a prefix of a stopped job.
histchars
[tab]Characters controlling history expansion and quick
[tab][tab]substitution. The first character is the history
[tab][tab]substitution character, usually `!'. The second is
[tab][tab]the `quick substitution' character, usually `^'. The
[tab][tab]third is the `history comment' character, usually `#'.
HISTIGNORE
[tab]A colon-separated list of patterns used to decide which
[tab][tab]commands should be saved on the history list.
