gistfile1.php

<?php     
$data = '<div>blabla<h1><a href="http://www.example.com/blabla.php?id=12345" class=l>blub</a></h1><h2><a href="http://www.example.com/asfadfafadf.php?id=12345" class=l>blub</a></h2>sdfafgdghaghagh<h1><a href="http://www.example.com/fdgadfhfh.php?id=123dsfasdf45" class=l>blub</a>asdfasdfasdf</h1>'; 
     
$doc = new DOMDocument();
$doc->loadHTML($data);
$xpath = new DOMXpath($doc);

$linkTargets = array();
foreach ($xpath->evaluate('//*[@href]/@href', NULL, FALSE) as $attribute) {
  $linkTargets[] = $attribute->value;
}
     
print_r($linkTargets);