Shell - help

help - Display information about shell builtin commands, 显示shell内置命令的帮助信息。

bash对每个shell内置命令都提供了帮助功能，使用help命令，将shell内置命令作为参数，就可以显示此shell内置命令的帮助信息。

在shell内置命令执行时，加上“--help”选项，也可以显示帮助信息。这两种方式都可以。

另外，许多可执行程序也支持"--help "选项，显示该命令支持的语法和选项的描述。

关于帮助信息的说明：

在中括号[]里的参数是可选参数，而竖线“|”则表示互斥的选项，只能从中选一个。

语法：

 

help [-dms] [pattern ...]

参数：

PATTERN - 指定一个要显示帮助信息的主题

返回值：

成功返回0；如果PATTERN没找到或参数不正确，返回失败。

常用选项

Option	Long Option	Meaning
-d		输出一个简单的功能说明。
-m		模范manpage的格式显示帮助信息。
-s		仅显示一个简短的语法使用格式说明。

示例

$ help -d help

help - Display information about builtin commands.

$ help -s help

help: help [-dms] [pattern ...]

$ help -m help

NAME

    help - Display information about builtin commands.

SYNOPSIS

    help [-dms] [pattern ...]

DESCRIPTION

    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 specifying a help topic

    

    Exit Status:

    Returns success unless PATTERN is not found or an invalid option is given.

SEE ALSO

    bash(1)

IMPLEMENTATION

    GNU bash, version 5.0.17(1)-release (x86_64-pc-linux-gnu)

    Copyright (C) 2019 Free Software Foundation, Inc.

    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

$ 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 specifying a help topic

    

    Exit Status:

    Returns success unless PATTERN is not found or an invalid option is given.

如果不加参数，则显示所有的help命令所支持的帮助主题：