Linux正则表达式范例

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,就是创建一个测试用的re-file文件,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.

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 'love\.'
  • 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loveLove
$ 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

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