You should probably use the suggested modules for this, but if you really want to do it otherwise, here's some code:

while ($text =~ /(href|<frame .*?src)[ ="']+(.*?)["'>]/g) {
    print $2;
}
[download]

Considering some of the nasty ways people can arrange their links, this is about as good as you can get. If you want to eliminate anything starting with command: other than http: (like mailto:), you can modify the above as follows:

while ($text =~ /(href|<frame .*?src)[ ="']+((http:)?[^:]*?)["'>]/g) {
    print $2;
}
[download]

If you find a link format that gets past this, feel free to post so I can update the regex.