17个案例带你3分钟搞定Linux正则表达式
作者丨ansheng
https://blog.ansheng.me/article/examples-of-linux-regular-expressions
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
<>
$ 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 | '\ |
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