Linux中如何使用帮助总结-白红宇

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~

本文转自zfz_linux_boy 51CTO博客，原文链接：http://blog.51cto.com/zhangfengzhe/1405530，如需转载请自行联系原作者