Linux 终端操作命令（2）内部命令分类

Linux 终端操作命令

也称Shell命令，是用户与操作系统内核进行交互的命令解释器，它接收用户输入的命令并将其传递给操作系统进行执行，可分为内部命令和外部命令。内部命令是Shell程序的一部分，而外部命令是独立于Shell的可执行程序。

内部命令

内部命令，实际上是shell程序的一部分，由shell程序识别并在shell程序内部完成运行，通常在Linux系统加载运行时shell就被加载并驻留在系统内存中。内部命令是写在bash源码里面的，因为解析内部命令shell不需要创建子进程，其执行速度比外部命令快。比如：alias， break， cd， echo， exit， pwd 等。

外部命令

外部命令是bash shell之外的程序，也并不是shell的一部分。外部命令位于/bin，/sbin， /usr/bin 或 /usr/sbin 等系统目录中。外部命令是Linux系统中的实用程序部分，因为实用程序的功能通常都比较强大，所以其包含的程序量也会很大，在系统加载时并不随系统一起被加载到内存中，而是在需要时才将其调用内存。通常外部命令的实体并不包含在shell中，但是其命令执行过程是由shell程序控制的。比如： awk， grep， ping，tar， vi 等。 除Linux系统自带的外部命令，通常需要安装对应的程序包才能使用，内部命令之外的所有可执行程序都可以被认作为外部命令。

内外部命令区别

内部命令在系统启动时就调入内存，是常驻内存的，所以执行效率高。

外部命令是系统的软件功能，用户需要时才从硬盘中读入内存，执行速度比内部命令慢。

内部命令列表

help命令可以列出所有内部命令：

hann@HannYang:~$ help
GNU bash, version 5.0.17(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 history -anrw [filename]>
 (( expression ))                                            if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMAN>
 . filename [arguments]                                      jobs [-lnprs] [jobspec ...] or jobs -x command [args]
 :                                                           kill [-s sigspec | -n signum | -sigspec] pid | jobspec .>
 [ arg... ]                                                  let arg [arg ...]
 [[ expression ]]                                            local [option] name[=value] ...
 alias [-p] [name[=value] ... ]                              logout [n]
 bg [job_spec ...]                                           mapfile [-d delim] [-n count] [-O origin] [-s count] [-t>
 bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u >  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]...) COMMANDS ;;]... esa>  read [-ers] [-a array] [-d delim] [-i text] [-n nchars] >
 cd [-L|[-P [-e]] [-@]] [dir]                                readarray [-d delim] [-n count] [-O origin] [-s count] [>
 command [-pVv] command [arg ...]                            readonly [-aAf] [name[=value] ...] or readonly -p
 compgen [-abcdefgjksuv] [-o option] [-A action] [-G globp>  return [n]
 complete [-abcdefgjksuv] [-pr] [-DEI] [-o option] [-A act>  select NAME [in WORDS ... ;] do COMMANDS; done
 compopt [-o|+o option] [-DEI] [name ...]                    set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
 continue [n]                                                shift [n]
 coproc [NAME] command [redirections]                        shopt [-pqsu] [-o] [optname ...]
 declare [-aAfFgilnrtux] [-p] [name[=value] ...]             source filename [arguments]
 dirs [-clpv] [+N] [-N]                                      suspend [-f]
 disown [-h] [-ar] [jobspec ... | pid ...]                   test [expr]
 echo [-neE] [arg ...]                                       time [-p] pipeline
 enable [-a] [-dnps] [-f filename] [name ...]                times
 eval [arg ...]                                              trap [-lp] [[arg] signal_spec ...]
 exec [-cl] [-a name] [command [arguments ...]] [redirecti>  true
 exit [n]                                                    type [-afptP] name [name ...]
 export [-fn] [name[=value] ...] or export -p                typeset [-aAfFgilnrtux] [-p] name[=value] ...
 false                                                       ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
 fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [c>  umask [-p] [-S] [mode]
 fg [job_spec]                                               unalias [-a] name [name ...]
 for NAME [in WORDS ... ] ; do COMMANDS; done                unset [-f] [-v] [-n] [name ...]
 for (( exp1; exp2; exp3 )); do COMMANDS; done               until COMMANDS; do COMMANDS; done
 function name { COMMANDS ; } or name () { COMMANDS ; }      variables - Names and meanings of some shell variables
 getopts optstring name [arg]                                wait [-fn] [id ...]
 hash [-lr] [-p pathname] [-dt] [name ...]                   while COMMANDS; do COMMANDS; done
 help [-dms] [pattern ...]                                   { COMMANDS ; }

通过整理以上内容，得到 68 个命令、函数、变量以及控制指令：

1	alias	alias [-p] [name[=value] ... ]
2	bg	bg [job_spec ...]
3	bind	bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u >
4	break	break [n]
5	builtin	builtin [shell-builtin [arg ...]]
6	caller	caller [expr]
7	case	case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esa>
8	cd	cd [-L|[-P [-e]] [-@]] [dir]
9	command	command [-pVv] command [arg ...]
10	compgen	compgen [-abcdefgjksuv] [-o option] [-A action] [-G globp>
11	complete	complete [-abcdefgjksuv] [-pr] [-DEI] [-o option] [-A act>
12	compopt	compopt [-o|+o option] [-DEI] [name ...]
13	continue	continue [n]
14	coproc	coproc [NAME] command [redirections]
15	declare	declare [-aAfFgilnrtux] [-p] [name[=value] ...]
16	dirs	dirs [-clpv] [+N] [-N]
17	disown	disown [-h] [-ar] [jobspec ... | pid ...]
18	echo	echo [-neE] [arg ...]
19	enable	enable [-a] [-dnps] [-f filename] [name ...]
20	eval	eval [arg ...]
21	exec	exec [-cl] [-a name] [command [arguments ...]] [redirecti>
22	exit	exit [n]
23	export	export [-fn] [name[=value] ...] or export -p
24	false	false
25	fc	fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [c>
26	fg	fg [job_spec]
27	for	for NAME [in WORDS ... ] ; do COMMANDS; done  for (( exp1; exp2; exp3 )); do COMMANDS; done
28	function	function name { COMMANDS ; } or name () { COMMANDS ; }
29	getopts	getopts optstring name [arg]
30	hash	hash [-lr] [-p pathname] [-dt] [name ...]
31	help	help [-dms] [pattern ...]
32	history	history [-c] [-d offset] [n] or history -anrw [filename]>
33	if	if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMAN>
34	jobs	jobs [-lnprs] [jobspec ...] or jobs -x command [args]
35	kill	kill [-s sigspec | -n signum | -sigspec] pid | jobspec .>
36	let	let arg [arg ...]
37	local	local [option] name[=value] ...
38	logout	logout [n]
39	mapfile	mapfile [-d delim] [-n count] [-O origin] [-s count] [-t>
40	popd	popd [-n] [+N | -N]
41	printf	printf [-v var] format [arguments]
42	pushd	pushd [-n] [+N | -N | dir]
43	pwd	pwd [-LP]
44	read	read [-ers] [-a array] [-d delim] [-i text] [-n nchars] >
45	readarray	readarray [-d delim] [-n count] [-O origin] [-s count] [>
46	readonly	readonly [-aAf] [name[=value] ...] or readonly -p
47	return	return [n]
48	select	select NAME [in WORDS ... ;] do COMMANDS; done
49	set	set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
50	shift	shift [n]
51	shopt	shopt [-pqsu] [-o] [optname ...]
52	source	source filename [arguments]
53	suspend	suspend [-f]
54	test	test [expr]
55	time	time [-p] pipeline
56	times	times
57	trap	trap [-lp] [[arg] signal_spec ...]
58	true	true
59	type	type [-afptP] name [name ...]
60	typeset	typeset [-aAfFgilnrtux] [-p] name[=value] ...
61	ulimit	ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
62	umask	umask [-p] [-S] [mode]
63	unalias	unalias [-a] name [name ...]
64	unset	unset [-f] [-v] [-n] [name ...]
65	until	until COMMANDS; do COMMANDS; done
66	variables	variables - Names and meanings of some shell variables
67	wait	wait [-fn] [id ...]
68	while	while COMMANDS; do COMMANDS; done

内部命令分类 

自己动手分类吧，具体分类明天继续......