前言
Shell有很多內置在其源代碼中的命令。這些命令是內置的，所以Shell不必到磁盤上搜索它們，執行速度因此加快。不同的Shell內置命令有所不同。
內置命令包含在 bash shell 本身里面。我該如何在 Linux / Apple OS X / *BSD / Unix 類操作系統列出所有的內置 bash 命令，而不用去讀大篇的 bash 操作說明頁？
shell 內置命令就是一個命令或一個函數，從 shell 中調用，它直接在 shell 中執行。 bash shell 直接執行該命令而無需調用其他程序。你可以使用 help 命令查看 Bash 內置命令的信息。以下是幾種不同類型的內置命令。
內置命令的類型
- Bourne Shell 內置命令：內置命令繼承自 Bourne Shell。
- Bash 內置命令：特定于 Bash 的內置命令表。
- 修改 Shell 行為：修改 shell 屬性和可選行為的內置命令。
- 特別的內置命令：由 POSIX 特別分類的內置命令。
如何查看所有 bash 內置命令
有以下的命令：
$ help
$ help | less
$ help | grep read
樣例輸出：
GNU bash, version 4.1.5(1)-release (x86_64-pc-linux-gnu)
These shell commands are defined internally. Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.
A star (*) next to a name means that the command is disabled.
job_spec [] history [-c] [-d offset] [n] or hist>
(( expression )) if COMMANDS; then COMMANDS; [ elif C>
. filename [arguments] jobs [-lnprs] [jobspec ...] or jobs >
: kill [-s sigspec | -n signum | -sigs>
[ arg... ] let arg [arg ...]
[[ expression ]] local [option] name[=value] ...
alias [-p] [name[=value] ... ] logout [n]
bg [job_spec ...] mapfile [-n count] [-O origin] [-s c>
bind [-lpvsPVS] [-m keymap] [-f filen> popd [-n] [+N | -N]
break [n] printf [-v var] format [arguments]
builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir]
caller [expr] pwd [-LP]
case WORD in [PATTERN [| PATTERN]...)> read [-ers] [-a array] [-d delim] [->
cd [-L|-P] [dir] readarray [-n count] [-O origin] [-s>
command [-pVv] command [arg ...] readonly [-af] [name[=value] ...] or>
compgen [-abcdefgjksuv] [-o option] > return [n]
complete [-abcdefgjksuv] [-pr] [-DE] > select NAME [in WORDS ... ;] do COMM>
compopt [-o|+o option] [-DE] [name ..> set [--abefhkmnptuvxBCHP] [-o option>
continue [n] shift [n]
coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]
declare [-aAfFilrtux] [-p] [name[=val> source filename [arguments]
dirs [-clpv] [+N] [-N] suspend [-f]
disown [-h] [-ar] [jobspec ...] test [expr]
echo [-neE] [arg ...] time [-p] pipeline
enable [-a] [-dnps] [-f filename] [na> times
eval [arg ...] trap [-lp] [[arg] signal_spec ...]
exec [-cl] [-a name] [command [argume> true
exit [n] type [-afptP] name [name ...]
export [-fn] [name[=value] ...] or ex> typeset [-aAfFilrtux] [-p] name[=val>
false ulimit [-SHacdefilmnpqrstuvx] [limit>
fc [-e ename] [-lnr] [first] [last] o> umask [-p] [-S] [mode]
fg [job_spec] unalias [-a] name [name ...]
for NAME [in WORDS ... ] ; do COMMAND> unset [-f] [-v] [name ...]
for (( exp1; exp2; exp3 )); do COMMAN> until COMMANDS; do COMMANDS; done
function name { COMMANDS ; } or name > variables - Names and meanings of so>
getopts optstring name [arg] wait [id]
hash [-lr] [-p pathname] [-dt] [name > while COMMANDS; do COMMANDS; done
help [-dms] [pattern ...] { COMMANDS ; }
另外一種選擇是使用下列命令：
compgen -b
compgen -b | more
查看 Bash 的內置命令信息
運行以下得到詳細信息：
要僅得到所有帶簡短描述的內置命令的列表，執行如下:
查找內置命令的語法和其他選項
使用下列語法去找出更多的相關內置命令：
help name
help cd
help fg
help for
help read
help :
樣例輸出：
:: :
Null command.
No effect; the command does nothing.
Exit Status:
Always succeeds
找出一個命令是內部的（內置）還是外部的
使用 type 命令或 command 命令：
type -a command-name-here
type -a cd
type -a uname
type -a :
type -a ls
或者：
type -a cd uname : ls uname
樣例輸出：
cd is a shell builtin
uname is /bin/uname
: is a shell builtin
ls is aliased to `ls --color=auto'
ls is /bin/ls
l is a function
l ()
{
ls --color=auto
}
或者：
command -V ls
command -V cd
command -V foo
View list bash built-ins command info on Linux or Unix
總結
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