--help: 是一个工具选项,可以用来显示一些工具的信息

    man : 可以显示系统手册页中的内容，这些内容大多数都是对命令的解释信息

    PS: () Space 键可以显示下一屏的文本信息

        ()  q 键是退出

    info:  是一个基于菜单的超文本系统，是由GNU项目开发并由Linux发布。

    info 工具包括一些关于Linux Shell,工具，GNU项目开发程序说明文档

    PS:  () ? 键可以列出info窗口中的相关命令

         () Space 键可以进行滚动浏览

File: dir       Node: Top       This is the top of the INFO tree

  This (the Directory node) gives a menu of major topics.

  Typing "q" exits, "?" lists all Info commands, "d" returns here,

  "h" gives a primer for first-timers,

  "mEmacs<Return>" visits the Emacs topic, etc.

  In Emacs, you can click mouse button  on a menu item or cross reference

  to select it.

* Menu: 

Archiving

* Cpio: (cpio).                 Copy-in-copy-out archiver to tape or disk.

* Tar: (tar).                   Making tape (or disk) archives.

Basics

* Common options: (coreutils)Common options.

                                Common options.

* Coreutils: (coreutils).       Core GNU (file, text, shell) utilities.

* Date input formats: (coreutils)Date input formats.

* File permissions: (coreutils)File permissions.

                                Access modes.

* Finding files: (find).        Operating on files matching certain criteria.

* ed: (ed).                     The GNU Line Editor.

Editors

* nano: (nano).                 Small and friendly text editor.

Emacs

* IDN Library: (libidn)Emacs API.

-----Info: (dir)Top,  lines --Top-----------------------------------------------------------------

Welcome to Info version 4.13. Type h for help, m for menu item.

[root@dep5 ~]# help

GNU bash, version 4.1.()-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] [n] or history -anrw [>

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

 . filename [arguments]                             jobs [-lnprs] [jobspec ...] or jobs -x command >

 :                                                  kill [-s sigspec | -n signum | -sigspec] pid | >

 [ 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] >

 bind [-lpvsPVS] [-m keymap] [-f filename] [-q na>  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>

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

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

 compgen [-abcdefgjksuv] [-o option]  [-A action]>  return [n]

 complete [-abcdefgjksuv] [-pr] [-DE] [-o option]>  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 [-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