前言
Shell有很多内置在其源代码中的命令。这些命令是内置的，所以Shell不必到磁盘上搜索它们，执行速度因此加快。不同的Shell内置命令有所不同。
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
- 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 -bcompgen -b | more
查看 Bash 的内置命令信息
运行以下得到详细信息：
help commandhelp 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 builtinuname is /bin/uname: is a shell builtinls is aliased to `ls --color=auto'ls is /bin/lsl is a functionl (){
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
总结
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对脚本之家的支持。
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