Linux命令(126)之help

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 -p
 compgen [-abcdefgjksuv] [-o option]  [-A action] [-G>  return [n]
 complete [-abcdefgjksuv] [-pr] [-DE] [-o option] [-A>  select NAME [in WORDS ... ;] do COMMANDS; done
 compopt [-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] pipeline
 enable [-a] [-dnps] [-f filename] [name ...]           times
 eval [arg ...]                                         trap [-lp] [[arg] signal_spec ...]
 exec [-cl] [-a name] [command [arguments ...]] [redi>  true
 exit [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; done
 function 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; done
 help [-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 is
    specified, 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 matching
    	PATTERN
    
    Arguments:
      PATTERN	Pattern specifiying a help topic
    
    Exit Status:
    Returns success unless PATTERN is not found or an invalid option is given.
[root@rhel77 ~]#