$ENV

Used only by interactive shells upon invocation; the value of $ENV is parameter-expanded. The result should be a full pathname for a file to be read and executed at startup. This is an XSI requirement.

$HOME

Home (login) directory.
使用者自己的目錄

$IFS

Internal field separator; i.e., the 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.

$LC_MESSAGES

Name of current language for output messages.

$LINENO

Line number in script or function of the line that just ran.

$NLSPATH

The location of message catalogs for messages in the language given by $LC_MESSAGES (XSI).

$PATH

Search path for commands.
執行命令時所搜尋的目錄

$PPID

Process ID of parent process.

$PS1

Primary command prompt string. Default is "$ ".
在命令列時的提示號

$PS2

Prompt string for line continuations. Default is "> ".
當命令尚未打完時，Shell 要求再輸入時的提示號

$PS4

Prompt string for execution tracing with set -x. Default is "+ ".

$PWD

Current working directory.

$TZ

時區

$MAILCHECK

每隔多少秒檢查是否有新的信件

$MANPATH

man 指令的搜尋路徑