标注：本教程只针对linux运维三剑客命令awk，sed，grep正则表达式

什么是正则表达式？

简单的说，正则表达式就是为处理大量的字符串而定义的一套规则和方法通过定义的这些特殊符号的辅助，系统管理员就可以快速过滤，替换或输出需要的字符串，linux正则表达式一般以行为单位处理

为什么要学会正则表达式?

在企业工作中，我们每天做的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、命令输出及日志文件等，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工作需要的特定字符串。这就要靠正则表达式。因此，可以说正则表达式就是为过滤这样字符串的需求而生Llinux最常应用的正则表达式的命令 grep(egrep)/sed/awk,换名话说linux三剑客要想能工作的更高效，那一定离不开正则表达式配合。

正则表达式注意事项

1、linux正则表达式一般以行为单位处理的

2、设置别名alias grep='grep

--color=auto',让匹配的内容显示颜色

3、注意字符集，使用LC_ALL=C，在/etc/profile配置文件最后添加一行export LC_ALL=C

4、注意使用单引号和双引号，建议使用双引号

举例(以grep为例子讲解)

[root@oldboy~]# cat file.txt

I amoldboy teacher!

Iteach linux.

Ilike badminton ball,billiard ball and chinese chess!

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

myqq num is 1300052.

not130000052.

mygod,i am not oldboy,but OLDBOY!

范例1：

[root@oldboy ~]# grep "^my"

file.txt

myblog is http://oldboy.blog.51cto.com

myqq num is 1300052.

mygod,i am not oldboy,but OLDBOY!

[root@oldboy ~]# grep "com$"

file.txt

myblog is http://oldboy.blog.51cto.com

[root@oldboy ~]# grep -n "^$"

file.txt

3:

8:

[root@oldboy ~]# grep "13...52"

file.txt

myqq num is 1300052.

[root@oldboy ~]# grep "//"

file.txt

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

[root@oldboy ~]# grep "\/\/"

file.txt

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

[root@oldboy ~]# grep '//' file.txt

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

[root@oldboy ~]# grep

"130*52" file.txt

myqq num is 1300052.

not130000052.

范例2：

[root@oldboy ~]# grep ".*"

file.txt

I amoldboy teacher!

Iteach linux.

Ilike badminton ball,billiard ball and chinese chess!

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

myqq num is 1300052.

not130000052.

mygod,i am not oldboy,but OLDBOY!

[root@oldboy ~]# grep "^my.*"

file.txt

myblog is http://oldboy.blog.51cto.com

myqq num is 1300052.

mygod,i am not oldboy,but OLDBOY!

[root@oldboy ~]# grep

"org.*$" file.txt

our

site is http://www.etiantian.org

[root@oldboy ~]# grep "[0-9]"

file.txt

myblog is http://oldboy.blog.51cto.com

myqq num is 1300052.

not130000052.

[root@oldboy ~]# grep

"[^a-z]" file.txt

I amoldboy teacher!

Iteach linux.

Ilike badminton ball,billiard ball and chinese chess!

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

myqq num is 1300052.

not130000052.

mygod,i am not oldboy,but OLDBOY!

范例3：

[root@oldboy ~]# grep -E

"0{4,5}" file.txt

not130000052.

[root@oldboy ~]# grep -E

"0{4,}" file.txt

not 130000052.

[root@oldboy ~]# grep -E

"0{3}" file.txt

myqq num is 1300052.

not130000052.

[root@oldboy ~]# grep -E

"0{,4}" file.txt

I amoldboy teacher!

Iteach linux.

Ilike badminton ball,billiard ball and chinese chess!

myblog is http://oldboy.blog.51cto.com

oursite is http://www.etiantian.org

myqq num is 1300052.

not130000052.

mygod,i am not oldboy,but OLDBOY!

范例4：

[root@oldboy ~]# echo 2oldboy >>

file.txt

[root@oldboy ~]# echo 3oldboy4 >>file.txt

[root@oldboy ~]# grep "oldboy"

file.txt

I amoldboy teacher!

myblog is http://oldboy.blog.51cto.com

mygod,i am not oldboy,but OLDBOY!

2oldboy

3oldboy4

[root@oldboy ~]# grep

"\boldboy" file.txt

I amoldboy teacher!

myblog is http://oldboy.blog.51cto.com

mygod,i am not oldboy,but OLDBOY!

[root@oldboy ~]# grep

"\boldboy\b" file.txt

I amoldboy teacher!

myblog is http://oldboy.blog.51cto.com

mygod,i am not oldboy,but OLDBOY!

范例5：

[root@oldboy ~]# grep -E

"[0-9]|qq|linux" file.txt

Iteach linux.

myblog is http://oldboy.blog.51cto.com

myqq num is 1300052.

not130000052.

2oldboy

3oldboy4

[root@oldboy ~]# egrep

"[0-9]|qq|linux" file.txt

Iteach linux.

myblog is http://oldboy.blog.51cto.com

myqq num is 1300052.

not130000052.

2oldboy

3oldboy4

Linux正则表达式结合三剑客企业级实践

1、取系统IP地址

替换功能

sed ‘s#支持正则位置##g’   file

sed -n ‘s#支持正则位置##gp’ file

[root@oldboy ~]# ifconfig eth3

eth3      Link encap:Ethernet  HWaddr 00:0C:29:A7:4E:51 

          inet addr:10.8.9.65  Bcast:10.8.9.255  Mask:255.255.255.0

          inet6 addr:fe80::20c:29ff:fea7:4e51/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500 Metric:1

          RX packets:134218 errors:0 dropped:0overruns:0 frame:0

          TX packets:31049 errors:0 dropped:0overruns:0 carrier:0

         collisions:0 txqueuelen:1000

          RX bytes:13502212 (12.8 MiB)  TX bytes:2379801 (2.2 MiB)

[root@oldboy ~]# ifconfig eth3 | sed -n'2p'|sed 's#^.*dr:##g'|sed 's#  B.*$##g'

10.8.9.65

[root@oldboy ~]# ifconfig eth3 | sed -n'2s#^.*dr:##gp' | sed 's#  B.*$##g'

10.8.9.65

2、sed后向引用

sed-n  's#()()#\1\2#gp'  file

当在前面匹配部分用小括号的时候，第一个括号内容，可以在后面的部分用\1输出。

第二个括号内容，可以在后面的部分用\2输出

[root@oldboy ~]# ifconfig eth3

eth3      Link encap:Ethernet  HWaddr 00:0C:29:A7:4E:51 

          inet addr:10.8.9.65  Bcast:10.8.9.255  Mask:255.255.255.0

          inet6 addr:fe80::20c:29ff:fea7:4e51/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500 Metric:1

          RX packets:134828 errors:0 dropped:0overruns:0 frame:0

          TX packets:31546 errors:0 dropped:0overruns:0 carrier:0

          collisions:0 txqueuelen:1000

          RX bytes:13565103 (12.9 MiB)  TX bytes:2431777 (2.3 MiB)

[root@oldboy ~]# ifconfig eth3 | sed-nr 's#^.*dr:(.*)  Bc.*$#\1#gp'

10.8.9.65

[root@oldboy ~]# stat /etc/hosts | sed

-nr 's#^.*ess: \((.*)\/-.*$#\1#gp'

0644

[root@oldboy ~]# sed -nr

's#([^:]+)(:.*:)(/.*$)#\3\2\1#gp' /etc/passwd | head -4

/bin/bash:x:0:0:root:/root:root

/sbin/nologin:x:1:1:bin:/bin:bin

/sbin/nologin:x:2:2:daemon:/sbin:daemon

/sbin/nologin:x:3:4:adm:/var/adm:adm