Use the URI module. It allows you to access bits of a URL without trying to hack a regular expression. Moreover, the code will be clearer (self-documenting).

Here is an example from the command line:

$ perl -wl -MURI -e '$url=URI->new("http://www.perlmonks.org/?parent=8
+39419;node_id=3333"); print $url->host;'
[download]

And the output:

www.perlmonks.org