shell 内置命令就是一个命令或一个函数，从 shell 中调用，它直接在 shell 中执行。 bash shell 直接执行该命令而无需调用其他程序。你可以使用 help 命令查看 bash 内置命令的信息。以下是几种不同类型的内置命令。
内置命令的类型
类型如下：
Bourne Shell 内置命令：内置命令继承自 Bourne Shell。
Bash 内置命令：特定于 Bash 的内置命令表。
修改 Shell 行为：修改 shell 属性和可选行为的内置命令。
特别的内置命令：由 POSIX 特别分类的内置命令。
如何查看所有 bash 内置命令
有以下的命令：
$ help $ help | less $ help | grep read
样例输出：
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 ; }
另外一种选择是使用下列命令：
compgen -b compgen -b | more
查看 Bash 的内置命令信息
运行以下得到详细信息：
help command help read
要仅得到所有带简短描述的内置命令的列表，执行如下:
$ help -d
查找内置命令的语法和其他选项
使用下列语法去找出更多的相关内置命令：
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help name help cd help fg help for help read help :
样例输出：
:: : Null command. No effect; the command does nothing. Exit Status: Always succeeds
找出一个命令是内部的（内置）还是外部的
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
样例输出：
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
作者：Vivek Gite
