Using URI is most likely more reliable than rolling your own regex, but in the interests of improving your knowledge of regexen the following may be of help:

use strict;
use warnings;

for (qw(http://www.url.com http://www.url.com/ http://www.url.com/cgi.
+pl?x=y)) {
    my $displayed_link = $_;

    $displayed_link =~ s!^.*?(\w*://[^/]+/?).*!$1!;
    print $displayed_link, "\n";
}
[download]

prints:

http://www.url.com
http://www.url.com/
http://www.url.com/
[download]