Linux中如何使用帮助总结

1.写在前面

   一直以来，虽然知道有问题问男人,对LINUX的帮助没有认真使用过，不会了就baidu,google，今天认真学习了下各种帮助命令，才知道自己的基本功有多么差。

2.使用帮助前

如果，我们想查看命令的帮助，应该首先确定这个命令的类型。

[root@localhost /]# type cd
cd is a shell builtin
[root@localhost /]# type su
su is /bin/su
[root@localhost /]#

Linux的命令分为两种：

内置命令（SHELL内置）

外部命令（文件系统上必定存在相应可执行文件）

使用type COMMAND的方式获取命令类型。

3.help or --help or man or info

通过确定命令类型后，我们就要选择命令来查看帮助了。

4.结论一：help COMMAND

[root@localhost /]# type cd
cd is a shell builtin
[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.
[root@localhost /]#

如果是内置命令，我们可以通过:

help COMMAND

来查看COMMAND命令的帮助。如果我们对内置命令使用man，则会出现：

BASH_BUILTINS(1) BASH_BUILTINS(1) NAME bash, :, ., [, 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, suspend, test, times, trap, type, typeset, ulimit, umask, unalias, unset, wait - bash built-in commands, see bash(1) BASH BUILTIN COMMANDS Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options. For exam- ple, the :, true, false, and test builtins do not accept options. : [arguments] No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned. . filename [arguments] source filename [arguments] Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not contain a slash, file names in PATH are used to find the directory containing filename. The file searched for in PATH need not be executable. When bash is not in posix mode, the current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if file- name is not found or cannot be read. alias [-p] [name[=value] ...] Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, an alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution when the alias is expanded. For each name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has been defined. bg [jobspec ...] Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the shell's notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with job control enabled, any specified jobspec was not found or was started without job control. bind [-m keymap] [-lpsvPSV] bind [-m keymap] [-q function] [-u function] [-r keyseq] bind [-m keymap] -f filename

上面实际上不是cd的帮助，而是BASH的介绍。

也就是说，对于内置命令，寻求帮助的途径是：

help COMMAND

5.结论二：man COMMAND

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 .. --author with -l, print the author of each file -b, --escape print octal escapes for nongraphic characters --block-size=SIZE use SIZE-byte blocks -B, --ignore-backups do not list implied entries ending with ~ -c with -lt: sort by, and show, ctime (time of last modification of file status information) with -l: show ctime and sort by name otherwise: sort by ctime -C list entries by columns --color[=WHEN]

对于外部命令，应该使用man，或者长选项--help的方式获取帮助。

[root@localhost /]# ls --help Usage: ls [OPTION]... [FILE]... 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 .. --author with -l, print the author of each file -b, --escape print octal escapes for nongraphic characters --block-size=SIZE use SIZE-byte blocks -B, --ignore-backups do not list implied entries ending with ~ -c with -lt: sort by, and show, ctime (time of last modification of file status information) with -l: show ctime and sort by name otherwise: sort by ctime -C list entries by columns --color[=WHEN] control whether color is used to distinguish file types. WHEN may be `never', `always', or `auto' -d, --directory list directory entries instead of contents, and do not dereference symbolic links -D, --dired generate output designed for Emacs' dired mode -f do not sort, enable -aU, disable -lst

6.man NUMBER COMMAND

man is manual

就像我们买了一些家电设备一样，都会有一个使用手册，这些手册都有一个目录结构，这样会方便用户查找。其实man也是分章节的。

1：User Commands（用户命令，所有用户可以使用的命令 /bin /usr/bin /usr/local/bin） 2：System Call(系统调用) 3：Library Call(库调用) 4：特殊文件（block file , character file。设备文件） 5：文件格式(解释COMMAND对应配置文件的语法格式) 6：games，游戏 7：杂项 8：管理命令（通常是管理员才有权限使用的命令/sbin /usr/sbin /usr/local/sbin）

查看具体的章节，直接man NUMBER COMMAND即可。

7.如何快速定位

通过前面的知识，我们知道，可以使用man来指定章节查看，可是如果内容过多，如何有效，快速定位到我们想要的内容呢？

下一页：SPACE 下一行：ENTER 上一页：b(before) 上一行: k 查找： /keyword 向下搜索 ?keyword 向上搜索 （默认不区分大小写） 搜索后，可能有多个 对/keyword而言 n 表示下一个 N 表示前一个 ?keyword恰好相反

8.关于info

info COMMAND

偏向命令的一些历史信息。如果可以man，就不用info了。

9.总结

学习完如何使用帮助后，然后独立解决了设置时间，感觉很好。

就算工作再怎么满，我也要挤出点时间学习，我相信我的LINUX水平会不断提高的~