- preg_replace: documentation ( source)
<?php
// transforms a U.S. date (MM/DD/YYYY) into a French date (DD/MM/YY)
$a1 = '04/23/0288'; // for test
$a2 = preg_replace("/([\d]+)\/([\d]+)\/[\d]{1}([\d]){2}/", "$2/$1/$3", $a1);
echo $a2; // must be '23/04/15'