Assuming protocol and all, it's pretty easy with Regexp::Common:

use Regexp::Common qw/URI/;
my @results;
while ($string =~/$RE{URI}{-keep}/g) {
    push @results, $1;
}
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Your sample seems to omit the protocol and other bits that make a URI. Do you know they are all http? Try looking at the regex from R::C::URI and pick out the host-and-domain part. It will start with two literal slashes and run until the next slash or space, whichever comes first.