For a more fun, but less portable and unrecommended solution...

link($oldfile, $newfile);
unlink($oldfile);
[download]

But you should really be using File::Copy as ar0n suggests.

Update: Which, of course, actually performs a rename and not a copy. So, it's doubly true that File::Copy should be used instead.

-><- -><- -><- -><- -><-
All things are Perfect
    To every last Flaw
    And bound in accord
         With Eris's Law
 - HBT; The Book of Advice, 1:7