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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.

Built-in Commands

.	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	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.

Built-In Commands (Chinese)

:	傳回零結束值。
.	從檔案參數讀取和執行指令，然後再傳回。
break	自含括的 for、while 或 until 指令迴圈跳出 (如果有的話)。
cd	將現行目錄變更至指定的目錄。
continue	回復含括的 for、while 或 until 指令迴圈的下一個疊代。
echo	將字元字串寫入標準輸出。
eval	讀取引數作為 shell 的輸入，然後執行結果指令。
exec	執行 Argument 參數所指定的指令，而非此 shell 所指定的指令，但不建立新的處理程序。
exit	結束由 n 參數來指定結束狀態的 shell。
export	標記名稱以便自動匯出至後續執行指令的環境。
hash	尋找和記住指定的指令，其搜尋路徑中的位置。
pwd	顯示現行目錄。
read	從標準輸入讀取一行。
readonly	將 Name 參數所指定的名稱標示為唯讀。
return	使函數結束，並傳回指定的傳回值。
set	控制各不同參數在標準輸出的顯示。
shift	將指令行引數向左移位。
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	解譯 shell 會以何種方式將指定的名稱解譯為指令名稱。
ulimit	顯示或調整配置的 shell 資源。
umask	決定檔案的許可權。
unset	移除指定的名稱所對應的變數或函數。
wait	等待指定的子程序結束，或報告它的終止狀態。