Linux基础正则表达式

什么是正则表达式？

正则表达式是为了处理大量的字符串而定义的一套规则和方法，例如：@代表123456，当我查找123455这几个字符的时候我就可以用@代替，这样速度更快，Linux正则一般为行为单位处理的。

为什么要用正则表达式？

在企业里，我们每天的Linux运维工作中，时刻都会面对大量带有字符串的文本配置，程序、命令及日志文件等，而我们经常会有迫切的需要，从大量的字符串内容中查找符合的字符串，

容易混淆的主事项

a.正则表达式应用非常广泛，存在各种语言中，列如：php,prl,java等，但是，我们今天讲的是系统运维工作中的正则表达式，即Linux表达式，最常应用的命令就是grep(egrep),sed,awk，换句话说Linux三剑客要像能工作的更高效，那一定离不开正则表达式的配合。

b.正则表达式和我们常用的通配符特殊字符有着本质区别；

注意事项：

a.LInux正则一般以行为单位处理的

b.alias grep=’grep –color=auto’，讲课是grep为咧。

c.注意字符集 LC_ALL=C

Linux基础正则表达式

基于grep来讲正则表达式，基础正则表达式.BRE(Basrc Regular Expression)

测试文件ansheng.txt内容：

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>

<span class="line">[root@centos6 ~]<span class="comment"># cat ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">I am a Linux Operation and Maintenance Engineer</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">I Hexo + Github made a static blog, blog address is: https://ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>
<span class="line">QQ: 6087414</span>
<span class="line">Thank you!</span>

符号	说明
^My	搜索以My开头的

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "^My" ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">My mail: as@ansheng.me</span>

符号	说明
me$	搜索以me结尾的

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "me$" ansheng.txt </span></span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>

符号	说明
^$	表示空格

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep -vn --color=auto "^$" ansheng.txt </span></span>
<span class="line">1:My name is quiet!</span>
<span class="line">2:I am a Linux Operation and Maintenance Engineer</span>
<span class="line">3:My youth will stay at eighteen</span>
<span class="line">4:I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">5:My mail: as@ansheng.me</span>
<span class="line">6:QQ: 6087414</span>
<span class="line">7:Thank you!</span>

符号	说明
.	代表且只能代表任意一个字符

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "." ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">I am a Linux Operation and Maintenance Engineer</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>
<span class="line">QQ: 6087414</span>
<span class="line">Thank you!</span>

全部都过滤出来了！

符号	说明
\	转义符，让有着特殊意义的字符变成没有任何意义的字符

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "\." ansheng.txt </span></span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>

只过滤包含.的行

符号	说明
*	重复0个或者多个前面的一个字符

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "0*" ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">I am a Linux Operation and Maintenance Engineer</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>
<span class="line">QQ: 6087414</span>
<span class="line">Thank you!</span>

符号	说明
.*	匹配任意字符

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto ".*" ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">I am a Linux Operation and Maintenance Engineer</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>
<span class="line">QQ: 6087414</span>
<span class="line">Thank you!</span>

.匹配的是任意一个字符，.*匹配的是任意0个或者个多个，所以才会有空行

符号	说明
[abc]	匹配字符集合内的任意一个字符

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
5
6
7

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "[abc]" ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">I am a Linux Operation and Maintenance Engineer</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>
<span class="line">Thank you!</span>

符号	说明
[^abc]	匹配不包含^后的任意字符的内容

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "[^abc]" ansheng.txt </span></span>
<span class="line">My name is quiet!</span>
<span class="line">I am a Linux Operation and Maintenance Engineer</span>
<span class="line">My youth will stay at eighteen</span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>
<span class="line">My mail: as@ansheng.me</span>
<span class="line">QQ: 6087414</span>
<span class="line">Thank you!</span>

符号	说明
a{n.m}	前面的字符重复N到M次

<span class="line">1</span>
<span class="line">2</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "4\{1,3\}" ansheng.txt  </span></span>
<span class="line">QQ: 6087414</span>

重复4一到三次

符号	说明
{n,}	前面的字符重复至少N次

<span class="line">1</span>
<span class="line">2</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "4\{1,\}" ansheng.txt  </span></span>
<span class="line">QQ: 6087414</span>

符号	说明
{n}	前面的字符重复N次

<span class="line">1</span>
<span class="line">2</span>

<span class="line">[root@ansheng ~]<span class="comment"># grep --color=auto "d\{2\}" ansheng.txt </span></span>
<span class="line">I Hexo + Github made a static blog, blog address is: https: //ansheng.me</span>

扩展的正则表达式（egrep或者grep -E）

扩展正则表达式 ERE Extended Regular Expressions

测试文件内容：

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>
<span class="line">5</span>
<span class="line">6</span>
<span class="line">7</span>
<span class="line">8</span>
9

<span class="line">[root@ansheng ~]<span class="comment"># cat linux.txt</span></span>
<span class="line">Linux is a good </span>
<span class="line">god assdxw bcvnbvbjk</span>
<span class="line">greatttttt  wexcvxc</span>
<span class="line">operaaaating  dhfghfvx</span>
<span class="line">gooodfs awrerdxxhkl</span>
<span class="line">gdsystem awxxxx</span>
<span class="line">glad</span>
<span class="line">good</span>

符号	说明
+	重复前一个字符一个或一个以上

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>

<span class="line">[root@ansheng ~]<span class="comment"># egrep --color=auto "go?d" linux.txt  </span></span>
<span class="line">god assdxw bcvnbvbjk</span>
<span class="line">gdsystem awxxxx</span>

符号	说明
？	0个或者一个字符

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>

<span class="line">[root@ansheng ~]<span class="comment"># egrep --color=auto "go?d" linux.txt   </span></span>
<span class="line">god assdxw bcvnbvbjk</span>
<span class="line">gdsystem awxxxx</span>

符号	说明
		表示或，查找多个字符串

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>

<span class="line">[root@ansheng ~]<span class="comment"># egrep --color=auto "gd|good" linux.txt </span></span>
<span class="line">Linux is a good </span>
<span class="line">gdsystem awxxxx</span>
<span class="line">good</span>

符号	说明
（）	分组过滤匹配

<span class="line">1</span>
<span class="line">2</span>
<span class="line">3</span>
<span class="line">4</span>

<span class="line">[root@ansheng ~]<span class="comment"># egrep --color=auto "g(la|oo)d" linux.txt </span></span>
<span class="line">Linux is a good </span>
<span class="line">glad</span>
<span class="line">good</span>

批注：上面的命令请自行加参数”–color=auto”，可以把过滤出来的字符串用颜色显示出来，我这里写的文档没有颜色的提示，如果要需要自己动手操作哦~

发表于：Linux

2016-07-12

# Linux

复制链接

Linux基础正则表达式

什么是正则表达式？

为什么要用正则表达式？

容易混淆的主事项

Linux基础正则表达式

扩展的正则表达式（egrep或者grep -E）

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哈哈，此处随缘！

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