- print_r: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$myinput = 'test <span>1234</span><span>12345</span>test<span>5678</span><span>12345</span>test';
preg_match_all("/<span>(\d{4})<\/span>/", $myinput, $myoutput);
print_r($myoutput);