Perl Regex to get the root domain of a URL

Question

How could I get some part of url?

For example:

http://www.facebook.com/xxxxxxxxxxx
http://www.stackoverflow.com/yyyyyyyyyyyyyyyy

I

Answer 1

I like the URI answer. The OP requested a regex, so in honor of the request and as a challenge, here is the answer I came up with. To be fair, sometimes it is not easy or feasible to install a CPAN modules. I have worked on some projects that are hardened using a very specific version of Perl and only certain modules are allowed.

Here is my attempt at the regex answer. Note that the www. is optional. Sub-domains like mobile. are honored. The search for / is not greedy therefore a URL with directories on the end will be parsed correctly. I am not dependent on the protocol; it could be http, https, file, sftp whatever. The output is captured in $1.

^.*://(?:[wW]{3}\.)?([^:/]*).*$

Sample input:

http://WWW.facebook.com:80/
http://facebook.com/xxxxxxxxxxx/aaaaa
http://www.stackoverflow.com/yyyyyyyyyyyyyyyy/aaaaaaa
https://mobile.yahoo.com/yyyyyyyyyyyyyyyy/aaaaaaa
http://www.theregister.co.uk/

Sample output:

facebook.com
facebook.com
stackoverflow.com
mobile.yahoo.com
theregister.co.uk

EDIT: Thanks @ikegami for the extra challenge. :) Now it supports WWW in any mixed case and a port number like :80.