grep、egrep以及正则表达式的使用

「爱情、让人受尽委屈。」 2022-08-14 04:35 221阅读 0赞

正则表达式是linux学习里面很重要的一部分内容，也算是一个难点，元字符多，组合方法也各种各样，每个人学习理解方法不一样，其中遇到的问题也各不相同，

学习正则表达式首先要会的是grep以及egrep命令的使用。

grep是Globalsearch Regular expression an Print out the line的缩写，是一种文本搜索的工具，可以根据用户指定的“模式（pattern）”对目标文本进行搜索过滤，显示出被“模式”匹配到的行。这里要

说的一点是，grep匹配到的是符合模式的一整行，例如一行中有2位数同时有3位数，模式中匹配的是2位数，这一行是会被匹配到的，

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      1 
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      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(255,20,147)!important">grep</code>&nbsp; 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">[OPTIONS]&nbsp;PATTERN&nbsp;[FILE...]</code> 
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<table style="padding:0px; margin:0px auto 10px; font-size:12px; border-collapse:collapse; color:rgb(80,80,80); font-family:宋体,'Arial Narrow',arial,serif"> 
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  <tr style="padding:0px; margin:0px"> 
   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">option</span></td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">作用</span></td> 
  </tr> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">-i<br style="padding:0px; margin:0px"> </span></td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配时忽略字符大小写</span></td> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">-o</span></td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">仅显示匹配到的内容</span></td> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">-v</span></td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">取反，显示没有匹配到的行</span></td> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">--color<br style="padding:0px; margin:0px"> </span></td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">高亮显示匹配到的内容<span style="padding:0px; margin:0px; line-height:0px"></span><span style="padding:0px; margin:0px; line-height:0px"></span><br style="padding:0px; margin:0px"> </span></td> 
  </tr> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">-A#</span></td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"><span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">显示出匹配的行之后的下文#行</span><br style="padding:0px; margin:0px"> </td> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">-B #</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"><span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">显示出匹配的行之前的上文#行</span><br style="padding:0px; margin:0px"> </td> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">-C #</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"><span style="padding:0px; margin:0px; line-height:0px"></span><span style="padding:0px; margin:0px; line-height:0px"></span>显示<span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">出匹配的行前后的#行</span><br style="padding:0px; margin:0px"> </td> 
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   <td align="left" style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> -E</td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)">使用扩展的正则表达式，后面会有介绍</td> 
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这只是一些常用的选项，具体使用过程中遇到，可以使用man命令查看

这仅仅是grep的简单用法，要想充分利用grep需要配合正则表达式。

正则表达式分为两类：

基本正则表达式

扩展正则表达式

基本正则表达式由能够实现不同功能的元字符组成，下面按照元字符不同的作用分别说明，为了方便看出匹配到的内容，我们先给grep一个别名，就是用上面的--color选项，能够高亮显示出匹配到的内容，匹配到的内容会以紫色显示。

字符匹配：用来对文本中的字符进行匹配的元字符

其中\[\]有几个特殊的表示方法

. : 匹配任意单个字符

[![112014\_1357\_grepegrep1.png][112014_1357_grepegrep1.png]][112014_1357_grepegrep1.png]

aab,ab,acb等都可以匹配到，即为搜索xlblog.txt中含有“ab中间有一个任意字符”的行

\[ \]:匹配指定集合中的任意单个字符;

\[\[:digit:\]\], \[0-9\]：匹配单个数字;

[![112014\_1357\_grepegrep2.png][112014_1357_grepegrep2.png]][112014_1357_grepegrep2.png]

\[\[:lower:\]\], \[a-z\]：匹配单个小写字母;

[![112014\_1357\_grepegrep3.png][112014_1357_grepegrep3.png]][112014_1357_grepegrep3.png]

\[\[:upper:\]\], \[A-Z\]：匹配单个大写字母;

[![112014\_1412\_grepegrep4.png][112014_1412_grepegrep4.png]][112014_1412_grepegrep4.png]

\[\[:alpha:\]\], \[a-zA-Z\]：匹配单个字母;

[![112014\_1357\_grepegrep5.png][112014_1357_grepegrep5.png]][112014_1357_grepegrep5.png]

\[\[:alnum:\]\], \[0-9a-zA-Z\]：匹配单个数字字母，两个都可以实现这个功能;

[![112014\_1412\_grepegrep6.png][112014_1412_grepegrep6.png]][112014_1412_grepegrep6.png]

\[\[:space:\]\]：匹配单个空格，这一行因为有个空白字符，所以被匹配出来了，因为是空白字符，就不能高亮显示了;

![spacer.gif][]

\[\[:punct:\]\]：即标点符号;

![spacer.gif][spacer.gif 1]

\[^\]:匹配指定集合外的任意单个字符，匹配任意非数字字母的字符，@和空白字符被匹配到了;

![spacer.gif][spacer.gif 2]

次数匹配，用于对前面紧邻的单个字符所能够出现的次数做出限定;

\*：匹配其前面的字符任一次，即表示0次、1次或多次;

[![112014\_1412\_grepegrep10.png][112014_1412_grepegrep10.png]][112014_1412_grepegrep10.png]

\*前面的字符a出现0次或者多次，而且其后紧跟字符b，所以ab,aab,aaaaab,bc等都可以匹配到，acb就不能匹配到，因为a与b之间不是相邻的。

\\?：匹配其前面的字符0次或者一次，这里要注意只有紫色的部分匹配到了，虽然前面有很多个a，但是因为ab匹配到了，所以整行显示出来了。

[  ![112014\_1412\_grepegrep11.png][112014_1412_grepegrep11.png]][112014_1412_grepegrep11.png]

\\+:匹配其前面的字符出现至少1次；

[![112014\_1357\_grepegrep12.png][112014_1357_grepegrep12.png]][112014_1357_grepegrep12.png]

\\\{m\\\}:匹配其前面的字符m次，这是准确到多少次;

[![112014\_1357\_grepegrep13.png][112014_1357_grepegrep13.png]][112014_1357_grepegrep13.png]

\\\{m,n\\\}：匹配其前面的字符至少m次，至多n次；

[ ![112014\_1412\_grepegrep14.png][112014_1412_grepegrep14.png]][112014_1412_grepegrep14.png]

ab，aab，aaab，aaaaaab像这样的都是可以匹配到的，对于aaaaab可能会有疑问，其实只是匹配到了aaab，因为aaab在aaaaaab这一行中，所以整行都显示出来了，紫色的部分是匹配到的内容。

那么“.\*”代表什么呢？很明显，匹配任意单个字符，所有的字符都被匹配到了；

[  ![112014\_1412\_grepegrep15.png][112014_1412_grepegrep15.png]][112014_1412_grepegrep15.png]

位置锚定：

^:  行首锚定，写在模式的最左侧， ^ab’ 即为匹配以a开头的后面跟了b的字符;

[![112014\_1412\_grepegrep16.png][112014_1412_grepegrep16.png]][112014_1412_grepegrep16.png]

$:行尾锚定，写在模式的最右侧，ab$’即为以b结尾前面有a的字符;

[![112014\_1412\_grepegrep17.png][112014_1412_grepegrep17.png]][112014_1412_grepegrep17.png]

^$: 空白行，这个很容易理解，行首遇到了行尾，那就是什么都没有了，即空白行;

[![112014\_1412\_grepegrep18.png][112014_1412_grepegrep18.png]][112014_1412_grepegrep18.png]

\\<:词首锚定, \\b，出现在要查找的单词模式的左侧;

“\\<ab”只有作为一个单词的词首的ab才能被匹配上，像xab，aab就不会匹配到;

![spacer.gif][spacer.gif 3]

\\>：词尾锚定, \\b，出现在要查找的单词模式的右侧;

“ab\\>”只有作为一个单词的词尾的ab才能匹配上 ;  ![spacer.gif][spacer.gif 4]

如cab，aaab，像abb，acb，abc就不能被匹配上;

\\<pattern\\>:匹配单词;

如：\\<abc\\>，即匹配单词abc，因为以a为词首以b为词尾中间是c的只能是单词abc![spacer.gif][spacer.gif 5]

分组：\$需要分组的内容\$,分组是为了后面可以引用前面模式匹配到的内容，这里就要介绍下后向引用的概念了。

后向引用：模式中，如果使用实现了分组，在某行文本的检查中，如果\$\$中的模式匹配到了

某内容，此内容后面的模式中可以被引用；

\\1,\\2, \\3

模式自左而右，引用第\#个左括号以及与其匹配右括号之间的模式匹配到的内容;

如：“\$a.c\$.\*\\1”：\$\$中匹配到的内容会被引用到后面的\\1的位置，前面匹配到了什么内容，后面也必须是这个内容;

abcxyabc，前面匹配到了abc那后面也必须是abc，axcxyabc，前面匹配到了axc，后面没有axc，所以这个字段不会被匹配到。

![spacer.gif][spacer.gif 6]

egrep及扩展的正则表达式

扩展正则表达式有两种使用方法

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   <td style="padding:0px!important; margin:0px!important; font-size:1em!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:inherit!important; color:rgb(175,175,175)!important"> 
    <div style="word-wrap:normal; padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      1 
    </div> </td> 
   <td style="height:26px; width:692px; padding:0px!important; margin:0px!important; font-size:1em!important; line-height:1.1em!important; float:none!important; border:0px!important; bottom:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:inherit!important"> 
    <div style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:relative!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
     <div style="white-space:nowrap; padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(0,130,0)!important">#&nbsp;egrep&nbsp;'pattern'&nbsp;file...</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

扩展正则表达式的元字符：

字符匹配：

扩展正则表达式的字符匹配是和正则表达式的一样的

次数匹配：

<table style="padding:0px; margin:0px auto 10px; font-size:12px; border-collapse:collapse; color:rgb(80,80,80); font-family:宋体,'Arial Narrow',arial,serif"> 
 <tbody style="padding:0px; margin:0px"> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">*</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面的字符任一次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">?</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面字符0次或1次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">+</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面的字符至少1次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">{m}</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面的字符m次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">{m,n}</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面的字符m-n次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">{m</span><span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">，}</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面的字符至少m次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">{0</span><span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">，n}</span><br style="padding:0px; margin:0px"> </td> 
   <td style="padding:5px 10px; margin:0px; border:1px solid rgb(221,221,221)"> <span style="padding:0px; margin:0px; font-family:微软雅黑,sans-serif">匹配其前面的字符0-n次</span><br style="padding:0px; margin:0px"> </td> 
  </tr> 
 </tbody> 
</table>

从这我们可以发现，扩展正则表达式只是将正则表达式的\\号去掉了而已，其他的用法都是一样的，\\在模式中起到了一个转译的作用，而在扩展正则表达式中则默认转译了，不需要在加转译符号

位置锚定：

扩展正则表达式的位置锚定也是和正则表达式一样的，这里的\\不能省略。

分组：

()：同样不需要转译符\\，也和正则表达式一样支持后向引用\\1,\\2\\3,…

或者：

a|b: a或者b

ab|cd：ab或者cd

这是扩展正则表达式所独有的元字符，表示“或者”，需要注意的是“|”符号左右两边是一个整体。

最后介绍一下fgrep

fgrep \[option\] 'string' file...

fgrep不支持正则表达式，只支持字符串的搜索，即string为什么匹配到的就是什么，是一种快速搜索文本的命令。

从上面可以看出扩展的正则表达式要比正则表达式简洁，而且还能实现更多的功能，所以我们要多多使用扩展正则表达式

[![041405283617635.gif][]][041405283617635.gif 1]

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[112014_1412_grepegrep11.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep11.png
[112014_1357_grepegrep12.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1357_grepegrep12.png
[112014_1357_grepegrep13.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1357_grepegrep13.png
[112014_1412_grepegrep14.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep14.png
[112014_1412_grepegrep15.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep15.png
[112014_1412_grepegrep16.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep16.png
[112014_1412_grepegrep17.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep17.png
[112014_1412_grepegrep18.png]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep18.png
[spacer.gif 3]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep19.png
[spacer.gif 4]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep20.png
[spacer.gif 5]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep21.png
[spacer.gif 6]: http://linuxu.qiniudn.com/wp-content/uploads/2014/11/112014_1412_grepegrep22.png
[041405283617635.gif]: /images/20220810/08af1b21871242058ccea3becb188f0d.png
[041405283617635.gif 1]: http://www.itmmd.com/boke.html