If capturing the link text after finding it so you can use it with the a method in CGI, then just use capturing parentheses in the regex.

$_ = 'some text http://moo.com fish';
/(http:\/\/)/
$href = $1;
[download]

For each pair of capturing parentheses (up to nine total), the text they capture is put into $1 through $9. Read perldoc perlre for more information about this and other regex stuff.

Of course, I'd recommend using some of the excellant solutions in this thread, but this is up to you.