[RegEx] regular expressions match IP addresses and domain names

Reprinted: http://blog.csdn.net/seawave/article/details/1520988

After reading several pages of mastering regular expression, I tried to write a regular expression that could match the IP string. I did not write a few lines of code to determine whether it was easy.

An IP string consisting of four segments, each of which is 0 ~ A decimal point. For example, 61.139.2.69 is a legal IP string.

If the regular expression is written as/d {1, 3} (/./d {1, 3}) {3}, It is not responsible because it can match an invalid IP string such as 300.400.555.666.

To match a 0 ~ There are several matching methods for the number between 255:

Match	Regular Expression	Description
0 ~ 9	/D	Single digit
10 ~ 99	[1-9]/d	Double digits
100 ~ 199	1/D/d	The number of three digits with one hundred bits
200 ~ 249	2 [0-4]/d	The number of three digits, the number of hundred digits is 2, and the number of digits is 0 ~ 9
250 ~ 255	25 [0-5]	The number of three digits, the number of hundred digits is 2, the number of ten digits is 5, and the number of single digits is 0 ~ 5

Write as a regular expression, that is: (/d | ([1-9]/d) | (1/D/d) | (2 [0-4]/D) | (25 [0-5]), but when such a regular expression matches strings like 254, it will match 2, 5, and 4 respectively to get three matches, if the expected results are not met, the correct method is to reverse the order to (25 [0-5]) | (2 [0-4]/d) | (1/D) | ([1-9]/d) |/d), because in the (xxx | YYY) Matching Behavior, It is searched from left to right.

The complete regular expression is:

(25 [0-5]) | (2 [0-4]/d) | (1/D/d) | ([1-9]/D) |/d )(/. (25 [0-5]) | (2 [0-4]/d) | (1/D/d) | ([1-9]/D) |/D) {3}

Press:

• A number with a high value of 0 such as 061 cannot be matched.
• It's too troublesome. It's easier to write a small piece of code for parsing.

 

A complete domain name consists of the root domain, top-level domain, level 2, level 3 ...... Domain names are separated by dots. Each domain name consists of letters, numbers, and minus signs (the first letter cannot be a minus sign). It is case-insensitive and cannot exceed 63 characters in length.

Obviously, a separate name can be matched by a regular expression [a-zA-Z0-9] [-a-zA-Z0-9] {}, and a complete domain name contains at least two names (such as Google.com, it is composed of Google and COM. At last, there can be a point that represents the root domain (in the specification, the last point is the complete domain name, however, it is generally considered that a domain name with more than two names is also a complete domain name, even if it is not followed ).

The regular expression that matches the complete Domain Name:

[A-zA-Z0-9] [-a-zA-Z0-9] {} (/. [a-zA-Z0-9] [-a-zA-Z0-9] {}) + /.?