You could use some high resolution time -

use Time::HiRes qw(gettimeofday);

$id = gettimeofday();
[download]

or if you've got time on your hands -

use Digest::MD5 qw(md5_hex);
use Time::HiRes qw(gettimeofday);
$id = md5_hex(gettimeofday());
[download]

Although you'll may have to download them from CPAN (here's Digest::MD5 and Time::HiRes)
HTH

broquaint