What are the Java regular expressions for matching IPv4 and IPv6 strings?

Question

Looking for a string to pass to String#matches(String) that will match IPv4, and another to match IPv6.

Answer 1

The regex allows the use of leading zeros in the IPv4 parts.

Some Unix and Mac distros convert those segments into octals.

I suggest using 25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d as an IPv4 segment.