Validating an IP with regex

Question

I need to validate an IP range that is in format 000000000 to 255255255 without any delimiters between the 3 groups of numbers. Each of the three groups that the final IP consists of should be 000 (yes, 0 padded) to 255.

As this is my 1st stackoverflow entry, please be lenient if I did not follow etiquette correctly.

Answer 1

This is a pretty common question. Here is a nice intro page on regexps, that has this case as an example. It includes the periods, but you can edit those out easily enough.

Answer 2

^([01]\d{2}|2[0-4]\d|25[0-5]){3}$

Which breaks down in the following parts:

1. 000-199
2. 200-249
3. 250-255

If you decide you want 4 octets instead of 3, just change the last {3} to {4}. Also, you should be aware of IPv6 too.

Answer 3

I would personally not use regex for this. I think it's easier to ensure that the string consists of 9 digits, split up the string into 3 groups of 3-digit numbers, and then check that each number is between 0 and 255, inclusive.

If you really insist on regex, then you could use something like this:

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

The expression comprises an alternation of three terms: the first matches 000-199, the second 200-249, the third 250-255. The {3} requires the match exactly three times.