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