IP地址的正则表达式精确解析

分段	正则表达式	解释
0-99	[1-9]?[0-9]	?表示前面[]中的内容可以取或不取
100-199	1[0-9]{2}	100到199的百位相同，十位个位都可以取0-9，使用{2}表示
200-249	2[0-4][0-9]
250-255	25[0-5]

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组合表示一个255使用|连接

([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])

ip地址格式：xxx.xxx.xxx.xxx(每个xxx表示一个0-255的数字)
观看规律发现 xxx.重复了三次,因此用下面的表示(.比较特殊因此需要反斜线转译）

(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}

完整的ip地址还缺少最后一个xxx
拼接上格式为

(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])

使用egrep或 grep -E 不需要对（）{}|转译，而使用grep必须转译
因此博主给了如下两种方式

grep -Eo "(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])" 
grep -o "\(\([1-9]\?[0-9]\|1[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)\.\)\{3\}\([1-9]\?[0-9]\|1[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)" 

测试结果：

[root@master etc]#ifconfig
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.106  netmask 255.255.255.0  broadcast 192.168.0.255
        inet6 fe80::8594:34ed:d5bf:7578  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:a6:81:72  txqueuelen 1000  (Ethernet)
        RX packets 3771121  bytes 321230571 (306.3 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 4390188  bytes 587011207 (559.8 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 40  bytes 3048 (2.9 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 40  bytes 3048 (2.9 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 192.168.122.1  netmask 255.255.255.0  broadcast 192.168.122.255
        ether 52:54:00:99:a5:a2  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
`[root@master etc]#ifconfig |grep -Eo "(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])" 
`192.168.0.106
255.255.255.0
192.168.0.255
127.0.0.1
255.0.0.0
192.168.122.1
255.255.255.0
192.168.122.255
`[root@master etc]#ifconfig |grep -o "\(\([1-9]\?[0-9]\|1[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)\.\)\{3\}\([1-9]\?[0-9]\|1[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)" 
`192.168.0.106
255.255.255.0
192.168.0.255
127.0.0.1
255.0.0.0
192.168.122.1
255.255.255.0
192.168.122.255

效果截图