<?php
$string = "list page.php?cpage=1, list page.php?cpage=2, list page.php?cpage=3 thats all";
preg_match_all("/cpage=[0-9]/", $string, $matches);
foreach($matches[0] as $value) {
$value = str_replace("?cpage=", "/", $value);
echo $value . '/';
}
//echo $string;
//hasil list page.php1, list page.php2, list page.php3 thats all
//yg diinginkan list page.php/1/, list page.php/2/, list page.php/3/ thats all