正则表达式是一种字符模式，用于在查找过程中匹配制定的字符。

元字符通常在 Linux 中分为两类：

1. Shell 元字符，由 Linux Shell 进行解析。
   
   

2. 正则表达式元字符，由 vi/grep/sed/awk 等文本处理工具进行解析。
   
   

正则表达式一般以文本行进行处理，在进行下面实例之前，先为 grep 命令设置 --color 参数：

$ alias grep='grep --color=auto'

这样每次过滤出来的字符串都会带色彩了。

在开始之前还需要做一件事情，就是创建两个测试用的文件 re-file 和 linux.txt，内容如下：

$ cat re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.


$ cat linux.txt
Linux is a good
god assdxw bcvnbvbjk
greatttttt  wexcvxc
operaaaating  dhfghfvx
gooodfs awrerdxxhkl
gdsystem awxxxx
glad
good

正则表达式元字符

• 特殊的元字符
  
  

• 扩展的正则表达式
  
  

实操

• 匹配以 love 开头的所有行
  

$ grep '^love' re-file
love, how much I adore you. Do you know

• 匹配 love 结尾的所有行
  

$ grep 'love$' re-file
clover. Did you see them?  I can only hope love.

• 匹配以 l 开头，中间包含两个字符，结尾是 e 的所有行
  

$ grep 'l..e' re-file
I had a lovely time on our little picnic.
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the

• 匹配 0 个或多个空行，后面是 love 的字符
  

$ grep ' *love' re-file
I had a lovely time on our little picnic.
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.

• 匹配 love 或 Love
  

$ grep '[Ll]ove' re-file  # 对l不区分大小写
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.

• 匹配 A-Z 的字母，其次是 ove
  

$ grep '[A-Z]ove' re-file
Lovers were all around us. It is springtime. Oh

• 匹配不在 A-Z 范围内的任何字符行，所有的小写字符
  

$ grep '[^A-Z]' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.

• 匹配 love.
  

$ grep 'love.' re-file
clover. Did you see them?  I can only hope love.

• 匹配空格
  

$ grep '^$' re-file

• 匹配任意字符
  

$ grep '.*' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.

• 前面 o 字符重复 2 到 4 次
  

$ grep 'o{2,4}' re-file
groove.

• 重复 o 字符至少 2 次
  

$ grep 'o{2,}' re-file
groove.

• 重复 o 字符最多 2 次
  

$ grep 'o{,2}' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.

• 重复前一个字符一个或一个以上
  

$ egrep "go+d" linux.txt
Linux is a good
god assdxw bcvnbvbjk
gooodfs awrerdxxhkl
good

• 0 个或者一个字符
  

$ egrep "go?d" linux.txt
god assdxw bcvnbvbjk
gdsystem awxxxx

• 同时查找多个字符串

$ egrep "gd|good" linux.txtLinux is a goodgdsystem awxxxxgood

• 分组过滤匹配
  

$ egrep "g(la|oo)d" linux.txt
Linux is a good
glad
good

来源：安生博客

原文：http://t.cn/AiNuhcKf

题图：来自谷歌图片搜索 

版权：本文版权归原作者所有

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