help和man查看命令帮助文档

在Linux系统中，命令太多，记全几乎不太可能，但是，我们可以通过help命令获取帮助。

命令语法:

help [选项] [命令]

其中,选项内容包括如下:

-d 显示命令简短主题描述

-s 显示命令简短语法描述

例如:

输入help命令回车后内容:

[root@bogon /]# help

GNU bash, version 4.1.2(1)-release (x86_64-redhat-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]
or history -anrw [filename>

(( expression )) if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMA>

. 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

bg [job_spec ...] mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] >

bind [-lpvsPVS] [-m keymap] [-f filename] [-q name] [-u > popd [-n] [+N | -N]

break
printf [-v var] format [arguments]

builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir]

caller [expr] pwd [-LP]

case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... es> read [-ers] [-a array] [-d delim] [-i text] [-n nchars]>

cd [-L|-P] [dir] readarray [-n count] [-O origin] [-s count] [-t] [-u fd>

command [-pVv] command [arg ...] readonly [-af] [name[=value] ...] or readonly -p

compgen [-abcdefgjksuv] [-o option] [-A action] [-G glo> return

complete [-abcdefgjksuv] [-pr] [-DE] [-o option] [-A act> select NAME [in WORDS ... ;] do COMMANDS; done

compopt [-o|+o option] [-DE] [name ...] set [--abefhkmnptuvxBCHP] [-o option-name] [arg ...]

continue
shift

coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]

declare [-aAfFilrtux] [-p] [name[=value] ...] 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] [name ...] times

eval [arg ...] trap [-lp] [[arg] signal_spec ...]

exec [-cl] [-a name] [command [arguments ...]] [redirect> true

exit
type [-afptP] name [name ...]

export [-fn] [name[=value] ...] or export -p typeset [-aAfFilrtux] [-p] name[=value] ...

false ulimit [-SHacdefilmnpqrstuvx] [limit]

fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [> umask [-p] [-S] [mode]

fg [job_spec] unalias [-a] name [name ...]

for NAME [in WORDS ... ] ; do COMMANDS; done unset [-f] [-v] [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 [id]

hash [-lr] [-p pathname] [-dt] [name ...] while COMMANDS; do COMMANDS; done

help [-dms] [pattern ...] { COMMANDS ; }

我们通过help命令查看某个命令帮助信息:



对于其他命令也一样，使用时不知道其含义，可以通过help命令查看帮助文档，获取帮助信息。

当然了，如果使用help还解决不了问题，我们可以使用man，查看在线手册，获取更多帮助信息：

man语法命令:

man [选项] [命令]

其中常用选项如下:

-a 显示所有的手册页，不只是显示第一个

-f 只显示命令的功能，而不显示详细的说明文件，跟whatis命令相同

-w 不显示手册内容，只显示将被格式化和显示的文件所在位置

例如:

[root@bogon /]# man pwd

回车后显示内容比help pwd显示的多，是在线手册，内容更丰富。

当我们看完文档时，通过按键盘上的q键，退出在线文档阅读。