Make it a sub?

sub get_img_test {
    return sprintf "height=19 width=15 src='/images/attach/%s.gif bord
+er=0", shift;
}

$img_url     = get_img_test('URL');
$img_unknown = get_img_test('UNKNOWN');
[download]

If you want it done with hash, use tie.

--
Tatsuhiko Miyagawa
miyagawa@cpan.org