How can I match IPv6 addresses with a Perl regex?
https://stackoverflow.com/questions/1802722
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So I need to match an ipv6 address which may or may not have a mask. Unfortunately I can't just use a library to parse the string.
The mask bit is easy enough, in this case:
(?:\/\d{1,3})?$/
The hard part is the different formats of an ipv6 address. It needs to match ::beef, beef::, beef::beef, etc.
An update: I'm almost there..
/^(\:\:([a-f0-9]{1,4}\:){0,6}?[a-f0-9]{0,4}|[a-f0-9]{1,4}(\:[a-f0-9]{1,4}){0,6}?\:\:|[a-f0-9]{1,4}(\:[a-f0-9]{1,4}){1,6}?\:\:([a-f0-9]{1,4}\:){1,6}?[a-f0-9]{1,4})(\/\d{1,3})?$/i
I am, in this case restricted to using perl's regex.
Solution
This contains a patch to Regexp::Common demonstrating a complete, accurate, tested IPv6 regex. Its a straight translation of the IPv6 grammar. Regexp::IPv6 is also accurate.
More importantly, it contains a test suite. Running it with your regex shows you're still a ways off. 10 out of 19 missed. 1 out of 12 false positives. IPv6 contains a lot of special shorthands making it very easy to get subtly wrong.
Best place to read up on what goes into an IPv6 address is RFC 3986 section 3.2.2.
OTHER TIPS
What do you mean you can't just use a library? How about a module? Regexp::IPv6 will give you what you need.
I'm not an IPv6 expert, but please trust me when I tell you that matching (let alone validating) IPv6 addresses is not easy with a very simple regex such as the one you suggest. There's many shorthands and various conventions for combining the address with a port, just to name an example. One such shorthand is that you can write 0:0:0:0:0:0:0:1 as ::1, but there's more. If you read German, I would suggest looking at the slides of Steffen Ullrich's talk at the 11th German Perl Workshop.
You say you can't use a library, but if you're going to reinvent the whole complexity of the library, then you could as well just import it verbatim into your project.
This mostly works...
^([0-9a-fA-F]{0,4}|0)(\:([0-9a-fA-F]{0,4}|0)){7}$
Cons: :: like cases not handled correctly
Try this:
^([0-9a-fA-F]{4}|0)(\:([0-9a-fA-F]{4}|0)){7}$
From Regular Expression Library: IPv6 address
You should also read this: A Regular Expression for IPv6 Addresses
If you need in perl check if a string is an IPv6 address you can try this:
if (/(([\da-f]{0,4}:{0,2}){1,8})/i) { print("$1") };
Try:
/^(((?=(?>.*?(::))(?!.+\3)))\3?|([\dA-F]{1,4}(\3|:(?!$)|$)|\2))(?4){5}((?4){2}|((2[0-4]|1\d|[1-9])?\d|25[0-5])(\.(?7)){3})\z/ai
here is the one worked for all the examples of IPv6 I've managed to find:
/^\s*((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:)))(%.+)?\s*$/
make sure it's the one line before using. it's been found here:
verified on all examples from the question page, the community page and the wikipedia site from here:
https://en.wikipedia.org/wiki/IPv6
the tool for the verification being used the one from here:
