linux常用命令-帮助命令-授之以渔

原创Blog，转载请注明出处

http://blog.csdn.net/hello_hwc

我的虚拟机系统是CentOS，版本较老，谅解

一、为什么要学习帮助命令？
  授人以鱼不如授人以渔，学会了怎么看帮助文档，是寻找到一个解决一类问题，而不是一个问题的方法。


二、常用的几个命名
1、man
-w 打印相关帮助文档的位置
-k 在man页中查找指定字符串和apropos命令相同
-f 和whatis相同

然后我们通过man ls命令来详细分析下man page中的内容

[root@localhost ~]# man ls
LS(1)                            User Commands                           LS(1)


NAME
       ls - list directory contents


SYNOPSIS
       ls [OPTION]... [FILE]...


DESCRIPTION
       List  information  about  the FILEs (the current directory by
       default).  Sort entries alphabetically if none  of  -cftuvSUX
       nor --sort.


       Mandatory  arguments  to long options are mandatory for short
       options too.


       -a, --all
              do not ignore entries starting with .


       -A, --almost-all
              do not list implied . and ..
...中间省略
AUTHOR
       Written by Richard Stallman and David MacKenzie.


REPORTING BUGS
       Report bugs to <[email protected]>.


COPYRIGHT
       Copyright © 2006 Free Software Foundation, Inc.
       This is free software.  You may  redistribute  copies  of  it
       under   the   terms   of   the  GNU  General  Public  License
       <http://www.gnu.org/licenses/gpl.html>.   There  is  NO  WAR-
       RANTY, to the extent permitted by law.


SEE ALSO
       The full documentation for ls is maintained as a Texinfo man-
       ual.  If the info and ls programs are properly  installed  at
       your site, the command


              info ls


       should give you access to the complete manual.


ls 5.97                          February 2010                           LS(1)

这里可以看到，info ls可以给出详细描述

首先会看到NAME，COPYRIGHT等每一部分的title，具体代表含义参照以下

NAME		名字，简单的命令是用来做什么的
SYNOPSIS	简短的指令使用语法
DESCRIPTION	详细的描述命令的使用方法
OPTIONS		针对SYNOPSIS，进行详细的阐述
COMMANDS	执行的时候可下达的命令
FILES		指令相关的文件
SEE ALSO	和这个指令相关的命令
EXAMPLE		范例
BUGS		尚存在的漏洞
COPYRIGHT	版权信息
REPORTING BUGS	发现Bug可以上传的邮箱
AUTHOR		作者

然后，又会看到LS（1）后面跟了一个1，这个数字也是有特定含义的

1	指令或者可执行文档
2	内核可调用的函数
3	常用函数库
4	档案说明
5	档案格式
6	游戏
7	linux系统的说明性内容
8	root可用的管理命名
9	和内核相关的文件

在man页中如何翻页，查找
箭头上下 上下行切换
Home/End 到第一页、最后一页
/String 查找一个字符串，n下一个查找到的结果，N上一个
q 结束这次
何时用man命令
我的心得是：这个命令基本不熟悉，需要详细的去看看自己想要的功能如何使用的时候，一般顺序是NAME-SYNOPSIS-DESCRIPTION-EXAMPLE


2、--help
列出常用命名的常用选项
使用场合：知道这个命令的使用领域，和简单使用方法，只是不熟悉某些选项

[root@localhost ~]# file --help
Usage: file [OPTION]... [FILE]...
Determine file type of FILEs.

  -m, --magic-file LIST      use LIST as a colon-separated list of magic
                               number files
  -z, --uncompress           try to look inside compressed files
  -b, --brief                do not prepend filenames to output lines
  -c, --checking-printout    print the parsed form of the magic file, use in
                               conjunction with -m to debug a new magic file
                               before installing it
  -f, --files-from FILE      read the filenames to be examined from FILE
  -F, --separator string     use string as separator instead of `:'
  -i, --mime                 output mime type strings
  -k, --keep-going           don't stop at the first match
  -L, --dereference          causes symlinks to be followed
  -n, --no-buffer            do not buffer output
  -N, --no-pad               do not pad output
  -p, --preserve-date        preserve access times on files
  -r, --raw                  don't translate unprintable chars to \ooo
  -s, --special-files        treat special (block/char devices) files as
                             ordinary ones
      --help                 display this help and exit
      --version              output version information and exit

3、whatis

查找whatis的数据库，寻找关键字的描述信息。在我们学会了man之后，可以直接man whatis来看信息

使用场合：我们想知道这个命令使用来干嘛的，或者我们想知道这个命令的种类

[root@localhost ~]# whatis ls
ls                   (1)  - list directory contents
ls                   (1p)  - list directory contents
[root@localhost ~]# whatis CD
cd                   (1p)  - change the working directory
cd [builtins]        (1)  - bash built-in commands, see bash(1)

4、help
查看shell内建指令的帮助信息，例如我们cd就是一个bash内建指令

[root@localhost ~]# cd --help
bash: cd: --: invalid option
cd: usage: cd [-L|-P] [dir]
[root@localhost ~]# help cd
cd: cd [-L|-P] [dir]
    Change the current directory to DIR.  The variable $HOME is the
    default DIR.  The variable CDPATH defines the search path for
    the directory containing DIR.  Alternative directory names in CDPATH
    are separated by a colon (:).  A null directory name is the same as
    the current directory, i.e. `.'.  If DIR begins with a slash (/),
    then CDPATH is not used.  If the directory is not found, and the
    shell option `cdable_vars' is set, then try the word as a variable
    name.  If that variable has a value, then cd to the value of that
    variable.  The -P option says to use the physical directory structure
    instead of following symbolic links; the -L option forces symbolic links
    to be followed.

其他的内建指令

alias, bg, bind, break, builtin, cd, command,
       compgen, complete,  continue,  declare,  dirs,  disown,  echo,
       enable, eval, exec, exit, export, fc, fg, getopts, hash, help,
       history, jobs, kill, let, local, logout, popd, printf,  pushd,
       pwd,  read,  readonly, return, set, shift, shopt, source, sus-
       pend, test, times, trap, type, typeset,  ulimit,  umask,  una-
       lias, unset, wait