Mine

<?php
$rand_string = rand(00000000,99999999);

$content = 'this is some test content for our theme system.\n';
$content = 'this is a new line\n';
$handle = fopen('/home/thesocialplanet/public_html/user_themes/'.$rand_string.'.theme.php', "w+");
fwrite($handle,$content);
fclose($handle);
?>