Usually it's best to use a module like Regexp::Common::URI or URI or Rose::URI to extract the path information.

If you are only interested in anything after the last slash, a regex should work fine:

if ($uri =~ m{([^/]+)\z}{
   print $1, $/;
}
[download]

Stripping the extension is a bit harder, because first you have to define what an extension is. If you just want to split off everything from the last period to the end, use a regex like this:

$filename =~ s/\.[^.]+\z//;
[download]

That will give you pkg-5.6.tar in the first example, which is technically correct, because you have a .tar file inside a .gz file. If you don't like that outcome, specify how the recognition of the extension should work.