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:

Shell元字符,由Linux Shell进行解析;
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,就是创建一个测试用的

$ 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.

文件内容摘录自<<UNIX/SHELL范例精解第四版>>

$ 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

元字符功能
^以什么开头
$以什么结尾
.匹配一个字符
*匹配0个或多个
[]匹配集合中的
[x-y]匹配集合范围内的
[^ ]匹配不在集合中的
\转义
  • 特殊的元字符
元字符功能实例怎么匹配
<以什么开头'<love'匹配以love开头的所有行
>以什么结尾'love>'匹配love结尾的所有行
\(..\)标签匹配以后使用的字符'(love)able \1er'用位置\1\2引导前面做好的标签,最大支持9个
x\{m\} or x\{m,\} or x\{m,n\}重复字符x,m次,至少m次,至少m且不超过n次o\{5,10\}o字符重复5到10次的行
  • 扩展的正则表达式
元字符说明
+重复前一个字符一个或一个以上
?0个或者一个字符
表示或,查找多个字符串
()分组过滤匹配

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0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
$ egrep "go+d" linux.txt
Linux is a good
god assdxw bcvnbvbjk
gooodfs awrerdxxhkl
good
  • 0个或者一个字符
ansheng@Ubuntu:/tmp$ egrep "go?d" linux.txt
god assdxw bcvnbvbjk
gdsystem awxxxx
  • 或,查找多个字符串
$ egrep "gd|good" linux.txt
Linux is a good
gdsystem awxxxx
good
  • 分组过滤匹配
$ egrep "g(la|oo)d" linux.txt
Linux is a good
glad
good

原作者:安生
本文转自:https://blog.ansheng.me/article/examples-of-linux-regular-expressions


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