内置命令包含在 bash shell 本身里面。我该如何在 Linux / Apple OS X / *BSD / Unix 类操作系统列出所有的内置 bash 命令，而不用去读大篇的 bash 操作说明页？

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

1. Bourne Shell 内置命令：内置命令继承自 Bourne Shell。
2. Bash 内置命令：特定于 Bash 的内置命令表。
3. 修改 Shell 行为：修改 shell 属性和可选行为的内置命令。
4. 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：

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

关于作者

作者是 nixCraft 网站的发起人和经验丰富的系统管理员，以及 Linux 操作系统/Unix shell 脚本编程培训师。他与全球客户以及包括 IT、教育、国防和空间研究以及非营利部门在内的各个行业合作。可以在 Twitter、Facebook、 Google+ 上关注他。

via: https://www.cyberciti.biz/faq/linux-unix-bash-shell-list-all-builtin-commands/

作者：Vivek Gite 译者：KarenMrzhang 校对：wxy

本文由 LCTT 原创编译，Linux中国 荣誉推出