grep使用正则表达式

谁践踏了优雅 2022-06-13 00:25 321阅读 0赞

**正则表达式**

> Regular Expressions is nothing but a pattern to match for each input line. A pattern is a sequence of characters. Following all are examples of pattern

^w1
    w1|w2
    [^ ]

**使用正则表达式**  
/etc/passwd中检索vivek

grep vivek /etc/passwd

示例输出

vivek:x:1000:1000:Vivek Gite,,,:/home/vivek:/bin/bash
    vivekgite:x:1001:1001::/home/vivekgite:/bin/sh
    gitevivek:x:1002:1002::/home/gitevivek:/bin/sh

忽略大小写

> grep -i -w vivek /etc/passwd

检索vivek或raj

> grep -E -i -w ‘vivek|raj’ /etc/passwd

**限定**  
通过**^**或者**$**来检索以特定字符开始或者结束的字串，比如：检索以vivek开始的字串写法如下：

> grep ^vivek /etc/passwd

示例输出

> vivek:x:1000:1000:Vivek Gite,,,:/home/vivek:/bin/bash  
> vivekgite:x:1001:1001::/home/vivekgite:/bin/sh

通过参数关键字**-w**实现完全匹配

> grep -w ^vivek /etc/passwd

以**foo**结尾

> grep ‘foo$’ filename

仅包含**foo**

> grep ‘^foo$’ filename

下面的命令可以检索空行

> grep ‘^$’ filename

**字符组、集**

> grep ‘\[vV\]ivek’ filename  
> grep ‘\[vV\]\[iI\]\[Vv\]\[Ee\]\[kK\]’ filename  
> grep -w ‘\[vV\]ivek\[0-9\]’ filename  
> grep ‘foo\[0-9\]\[0-9\]’ filename  
> grep ‘\[A-Za-z\]’ filename  
> grep \[wn\] filename

中括号表达式

*  \[:alnum:\] – 字母数字
 *  \[:alpha:\] – 英文字符
 *  \[:blank:\] – 空字符: space and tab.
 *  \[:digit:\] – 阿拉伯数字: ‘0 1 2 3 4 5 6 7 8 9’.
 *  \[:lower:\] – 小写字符: ‘a b c d e f g h i j k l m n o p q r s t u v w x y z’.
 *  \[:space:\] – 空格字符: tab, newline, vertical tab, form feed, carriage return, and space.
 *  \[:upper:\] – 大写字符: ‘A B C D E F G H I J K L M N O P Q R S T U V W X Y Z’.

> grep ‘\[:upper:\]’ filename

**通配符**  
**.**匹配单个字符

grep '\<b.t\>' filename

*  **\\<** 匹配词首空串
 *  **>** 匹配词尾空串

检索仅包含两个字母的字串

> grep ‘^..$’ filename

检索以.和数字开头的字串

> grep ‘^.\[0-9\]’ filename

**转义.号**  
检索ip地址 **192.168.1.254**的命令无效的，

> grep ‘192.168.1.254’ /etc/hosts

三个**.**号均需要转义

> grep ‘192.168.1.254’ /etc/hosts

检索匹配通用的IP地址

> egrep ‘\[\[:digit:\]\]\{1,3\}.\[\[:digit:\]\]\{1,3\}.\[\[:digit:\]\]\{1,3\}.\[\[:digit:\]\]\{1,3\}’ filename

**检索包含破折号的字符**  
使用关键字**-e**，比如检索**-test-**

> grep -e ‘–test–’ filename

**使用OR选项**

> grep -E ‘word1|word2’ filename  
> egrep ‘word1|word2’ filename

或者

grep 'word1\|word2' filename

**使用AND选项**

grep 'word1' filename | grep 'word2'

**字符重复次数**

> \{N\}  
> \{N,\}  
> \{min,max\}

egrep "v{2}" filename
    egrep 'co{1,2}l' filename
    egrep 'c{3,}' filename

检索通用手机号码，格式： 91-1234567890

> grep “\[\[:digit:\]\]\{2\}\[ -\]\\?\[\[:digit:\]\]\{10\}” filename

**突出显示检索结果**

grep --color regex filename

**只显示匹配内容，不显示匹配行**

grep -o regex filename

**正则表达式**

<table> 
 <thead> 
  <tr> 
   <th>Regex operator</th> 
   <th>Meaning</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>.</td> 
   <td>Matches any single character.</td> 
  </tr> 
  <tr> 
   <td>?</td> 
   <td>The preceding item is optional and will be matched, at most, once.</td> 
  </tr> 
  <tr> 
   <td>*</td> 
   <td>The preceding item will be matched zero or more times.</td> 
  </tr> 
  <tr> 
   <td>+</td> 
   <td>The preceding item will be matched one or more times.</td> 
  </tr> 
  <tr> 
   <td>{N}</td> 
   <td>The preceding item is matched exactly N times.</td> 
  </tr> 
  <tr> 
   <td>{N,}</td> 
   <td>The preceding item is matched N or more times.</td> 
  </tr> 
  <tr> 
   <td>{N,M}</td> 
   <td>The preceding item is matched at least N times, but not more than M times.</td> 
  </tr> 
  <tr> 
   <td>–</td> 
   <td>Represents the range if it’s not first or last in a list or the ending point of a range in a list.</td> 
  </tr> 
  <tr> 
   <td>^</td> 
   <td>Matches the empty string at the beginning of a line; also represents the characters not in the range of a list.</td> 
  </tr> 
  <tr> 
   <td>$</td> 
   <td>Matches the empty string at the end of a line.</td> 
  </tr> 
  <tr> 
   <td>\b</td> 
   <td>Matches the empty string at the edge of a word.</td> 
  </tr> 
  <tr> 
   <td>\B</td> 
   <td>Matches the empty string provided it’s not at the edge of a word.</td> 
  </tr> 
  <tr> 
   <td>\&lt;</td> 
   <td>Match the empty string at the beginning of word.</td> 
  </tr> 
  <tr> 
   <td>&gt;</td> 
   <td>Match the empty string at the end of word.</td> 
  </tr> 
 </tbody> 
</table>

**grep vs egrep**  
egrep与grep -E等价，其会将PATTERN翻译成扩展的正则表达式  
![这里写图片描述][SouthEast]  
[https://www.cyberciti.biz/faq/grep-regular-expressions/][https_www.cyberciti.biz_faq_grep-regular-expressions]

[SouthEast]: /images/20220613/ff406a80a4c5406e98f67a8123e987df.png
[https_www.cyberciti.biz_faq_grep-regular-expressions]: https://www.cyberciti.biz/faq/grep-regular-expressions/