linux命令之help

1.help介绍

linux命令help用来显示内置命令的帮助信息

2.help用法

help [参数] command

help参数 参数说明-d输出每个命令的简短描述-m以手册页格式显示命令用法-s仅输出每个匹配命令的简短使用概要

3.实例

3.1.以手册页格式显示命令用法

命令：

help -m

[root@rhel77 ~]# help -m
GNU bash, version 4.2.46(2)-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] [n] or history -anrw [file>(( expression ))                                       if COMMANDS; then COMMANDS; [ elif COMMANDS; then C>. filename [arguments]                                 jobs [-lnprs] [jobspec ...] or jobs -x command [arg>:                                                      kill [-s sigspec | -n signum | -sigspec] pid | jobs>[ arg... ]                                             let arg [arg ...][[ expression ]]                                       local [option] name[=value] ...alias [-p] [name[=value] ... ]                         logout [n]bg [job_spec ...]                                      mapfile [-n count] [-O origin] [-s count] [-t] [-u >bind [-lpvsPVS] [-m keymap] [-f filename] [-q name] >  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 ;;]..>  read [-ers] [-a array] [-d delim] [-i text] [-n nch>cd [-L|[-P [-e]]] [dir]                                readarray [-n count] [-O origin] [-s count] [-t] [->command [-pVv] command [arg ...]                       readonly [-aAf] [name[=value] ...] or readonly -pcompgen [-abcdefgjksuv] [-o option]  [-A action] [-G>  return [n]complete [-abcdefgjksuv] [-pr] [-DE] [-o option] [-A>  select NAME [in WORDS ... ;] do COMMANDS; donecompopt [-o|+o option] [-DE] [name ...]                set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg>continue [n]                                           shift [n]coproc [NAME] command [redirections]                   shopt [-pqsu] [-o] [optname ...]declare [-aAfFgilrtux] [-p] [name[=value] ...]         source filename [arguments]dirs [-clpv] [+N] [-N]                                 suspend [-f]disown [-h] [-ar] [jobspec ...]                        test [expr]echo [-neE] [arg ...]                                  time [-p] pipelineenable [-a] [-dnps] [-f filename] [name ...]           timeseval [arg ...]                                         trap [-lp] [[arg] signal_spec ...]exec [-cl] [-a name] [command [arguments ...]] [redi>  trueexit [n]                                               type [-afptP] name [name ...]export [-fn] [name[=value] ...] or export -p           typeset [-aAfFgilrtux] [-p] name[=value] ...false                                                  ulimit [-SHacdefilmnpqrstuvx] [limit]fc [-e ename] [-lnr] [first] [last] or fc -s [pat=re>  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; donefunction name { COMMANDS ; } or name () { COMMANDS ;>  variables - Names and meanings of some shell variab>getopts optstring name [arg]                           wait [id]hash [-lr] [-p pathname] [-dt] [name ...]              while COMMANDS; do COMMANDS; donehelp [-dms] [pattern ...]                              { COMMANDS ; }
[root@rhel77 ~]# 

3.2.输出内置命令的简短描述

命令：

help -d fg

[root@rhel77 ~]# help -d fg
fg - Move job to the foreground.
[root@rhel77 ~]# 

3.3.仅输出内置命令的简短使用概要

命令：

help -s fg

[root@rhel77 ~]# help -s fg
fg: fg [job_spec]
[root@rhel77 ~]# 

3.4.显示help命令的用法

命令：

help help

[root@rhel77 ~]# help help
help: help [-dms] [pattern ...]Display information about builtin commands.Displays brief summaries of builtin commands.  If PATTERN isspecified, gives detailed help on all commands matching PATTERN,otherwise the list of help topics is printed.Options:-d	output short description for each topic-m	display usage in pseudo-manpage format-s	output only a short usage synopsis for each topic matchingPATTERNArguments:PATTERN	Pattern specifiying a help topicExit Status:Returns success unless PATTERN is not found or an invalid option is given.
[root@rhel77 ~]#