Here is a way to do it without regex
Code:
$dom = new DOMDocument();
@$dom->loadHTML($html);
$xpath = new DOMXPath($dom);
$baseNodes = $xpath->evaluate("//base/@href");
if ($baseNodes->length == 1) {
$baseUrl = rtrim($baseNodes->item(0)->nodeValue, '/');
}
$hrefs = $xpath->evaluate("//a");