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Shells

bash	The GNU Project's Bourne-Again Shell.
ksh	The Korn shell, either an original or clone, depending upon the operating system.
pdksh	The Public Domain Korn shell.
sh	The original Bourne shell, particularly on commercial Unix systems.
zsh	The Z-shell.

系統內建指令

指令	意義
:	不做事，單純傳回'0'結束值(執行成功)
·	將後面帶的字串當作 Shell script 請Current Shell 執行之
break	自涵括的 for, while 或 until 指令迴圈中跳出 (如果有的話)
cd	將現行目錄變更至指定的目錄
continue	回復涵括的 for、while 或 until 指令迴圈的下一個回合
echo	將後面帶的字串於 STDOUT 印出
eval	將後面帶的字串作為指令由一個新的子程序執行之
exec	將後面帶的字串作為指令由Current Shell的程序執行之，任務結束時，該程序立即中止。 (一個可能的應用是: 換一個自己喜歡的Shell，踢掉原有的Shell)
exit <n>	中止Current Shell，並指定結束狀態為 'n'
export	將變數設為環境變數
hash	記住指令的路徑以加速指令的執行
pwd	顯示現行目錄
read	從標準輸入讀取一行
readonly	將變數設定為唯讀
return	結束函數，並傳回 exit code
set	顯示所有變數及其內容
shift	將位置變數向左移 n 位
test	評估條件表示式
times	顯示執行 shell 之處理程序的使用者和系統累計次數
trap	當 shell 收到指定的信號時，執行指定的指令
type	解釋 shell 會以何種方式執行 (內建指令，或外部指令的完整路徑)
ulimit	顯示或調整配置的 shell 資源
umask	設定所有新建檔案的預設權限
unset	移除變數或函數
wait	等待指定的子程序結束，或報告它的終止狀態

Built-in Commands (English)

.	Read and execute a given file, in the current shell.
break	Break out of a for, select, until, or while loop.
cd	Change the current directory.
command	Bypass the search for functions to run a regular built-in command.
continue	Start the next iteration of a for, select, until, or while loop.
eval	Evaluate given text as a shell command.
exec	With no arguments, change the shell's open files. With arguments, replace the shell with another program.
exit	Exit a shell script, optionally with a specific exit code.
export <var>	Export a variable into the environment of subsequent programs.
false	Do nothing, unsuccessfully. For use in shell loops.
getopts	Process command-line options.
read	Read lines of input into one or more shell variables.
readonly	Mark a variable as read-only; i.e., unchangeable.
return	Return a value from a shell function.
set	Print shell variables and values; set shell options; set the command-line parameters ($1, $2, ...).
shift	Move the command-line parameters down by one or more.
test	Evaluate expressions, which may be string-, numeric-, or file-attribute-related.
trap	Manage operating system signals.
true	Do nothing, successfully. For use in shell loops.
type	Indicate the nature of a command (keyword, built-in, external, etc.).
typeset	Declare variables and manage their type and attributes.
ulimit	Set or display various per-process system-imposed limits.
unset	Remove shell variables and functions.

Some Useful Commands

The following commands are useful in day-to-day shell scripting:

basename	Print the last component of a pathname, optionally removing a suffix. Mainly used in command substitution.
dirname	Print all but the last component of a pathname. Mainly used in command substitution.
env	Manipulate the environment of a command.
id	Print user and group ID and name information.
date	Print the current date and time, optionally under control of a user-supplied format string.
who	Print a list of logged-on users.
stty	Manipulate the state of the current terminal device.