- var_dump: documentation ( source)
- preg_match: documentation ( source)
- implode: documentation ( source)
- range: documentation ( source)
<?php
var_dump(range(1, 31));die;
$date = "4/23/15";
preg_match('~^1|2|3|4\/' . implode('|', range(1, 31)) . '\/[0-9]{2}$~', $date, $m);
var_dump($m);