IP地址/主机名匹配正则表达式

Question

I need to match two ipaddress/hostname with a regular expression : Like 20.20.20.20

should match with      20.20.20.20
should match with      [http://20.20.20.20/abcd]
should not match with  20.20.20.200
should not match with  [http://20.20.20.200/abcd]
should not match with  [http://120.20.20.20/abcd]
should match with      AB_20.20.20.20
should match with      20.20.20.20_AB

At present i am using something like this regular expression: "(.*[^(\\w)]|^)20.20.20.20([^(\\w)].*|$)" But it is not working for the last two cases. As the "\\w" is equal to [a-zA-Z0-9_]. Here I also want to eliminate the "_" underscore. I tried different combination but not able to succeed. Please help me with this regular expression.

Answer 1

(.*[_]|[^(\w)]|^)10.10.10.10([_]|[^(\w)].*|$)

我花了更多时间在这个上，这个正则表达式似乎起作用了。

Answer 2

I don't know which language you're using, but with Perl-like regular expressions you could use the following, shorter expression:

(?:\b|\D)20\.20\.20\.20(?:\b|\D)

This effectively says:

1. Match word boundary ( \\b , here: the start of the word) or a non-digit ( \\D ).
2. Match IP address.
3. Match word boundary ( \\b , here: the end of the word) or a non-digit ( \\D ).

Note 1: ?: causes the grouping (\\b|\\D) not to create a backreference, ie to store what it has found. You probably don't need the word boundaries/non-digits to be stored. If you actually need them stored, just remove the two ?: s.

Note 2: This might be nit-picking, but you need to escape the dots in the IP address part of the regular expression, otherwise you'd also match any other character at those positions. Using 20.20.20.20 instead of 20\\.20\\.20\\.20 , you might for example match a line carrying a timestamp when you're searching through a log file...

2012-07-18 20:20:20,20  INFO  Application startup successful, IP=20.20.20.200

...even though you're looking for IP addresses and that particular one ( 20.20.20.200 ) explicitly shouldn't match, according to your question. Admittedly though, this example is quite an edge case.