for my $id (0 .. 100000)
{
    $ua->get($url."?id=21&extern_eid=".(09-$id))
    //rest of the code
} 


##</code><code>##


for my $i (0..10000) {
  $ua->get('http://www-db.sn.schule.de/index.php', id => 21, extern_uid => $i);
  # process reply
}