Apart from the advice you have already had about URLs, don't write a regular expression to find email addresses - use Email::Find

Update: lhoward's advice is good. Be careful if your input is HTML because your regular expression will display the link twice if it's html that already has links. e.g.:

<a href="http://www.perlmonks.org">http://www.perlmonks.org</a>
[download]

With arturo's regular expression, you will get:

<a href="http://<a href="www.perlmonks.org"></a>">http://<a href="www.
+perlmonks.org"></a></a>
[download]

or something like that.

$ perldoc perldoc