I wish Regexp::Common had a $RE{net}{IPv6} regular expression, but it doesn't (yet).

So I tried to implement this myself, but ripped off the IPv6 matching bit from the existing Regexp::IPv6 which happens to have a working IPv6 regular expression with a reasonable test suite. Now, why Regexp::IPv6 is not part of Regexp::Common?

By the way, I'll copy/paste the full regular expression to match IPv6 addresses, just for fun:

:(?::[0-9a-fA-F]{1,4}){0,5}(?:(?::[0-9a-fA-F]{1,4}){1,2}|:(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.]
(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?
[0-9]{1,2})))|[0-9a-fA-F]{1,4}:(?:[0-9a-fA-F]{1,4}:(?:[0-9a-fA-F]{1,4}:(?:[0-9a-fA-F]{1,4}:(?:[0-9a-fA-F]{1,4}:(?:
[0-9a-fA-F]{1,4}:(?:[0-9a-fA-F]{1,4}:(?:[0-9a-fA-F]{1,4}|:)|(?::(?:[0-9a-fA-F]{1,4})?|(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?
[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4]
[0-9]|[0-1]?[0-9]{1,2}))))|:(?:(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})
[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))|[0-9a-fA-F]{1,4}(?::[0-9a-fA-F]
{1,4})?|))|(?::(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|
2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))|:[0-9a-fA-F]{1,4}(?::(?:(?:25[0-5]|2[0-4]
[0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.]
(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))|(?::[0-9a-fA-F]{1,4}){0,2})|:))|(?:(?::[0-9a-fA-F]{1,4}){0,2}(?::(?:
(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?
[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))|(?::[0-9a-fA-F]{1,4}){1,2})|:))|(?:(?::[0-9a-fA-F]{1,4}){0,3}
(?::(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|
[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))|(?::[0-9a-fA-F]{1,4}){1,2})|:))|(?:(?::[0-9a-fA-F]{1,4})
{0,4}(?::(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4]
[0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))|(?::[0-9a-fA-F]{1,4}){1,2})|:))

Of course, I will never be able to tell if it's right or wrong, but the fact is that it passes the test suite :)
However, the actual code is not like that: it generates the full regular expression from a few components. Anyway, I've pushed a ipv6 branch on my fork of Regexp::Common. I hope it will be included soon in Regexp::Common or improved it enough to be included in it, so we can finally match IPv6 addresses with:

use Regexp::Common;

my $addr = '2001:0db8:0000:0000:0000:0000:1428:57ab';
if ($addr =~ $RE{net}{IPv6}) {
    print "Yes, it is an IPv6 address";
}
else {
    print "No, it isn't";
}