使用simplexml

using simplexml

$html = '<link type="text/html" rel="alternate" href="http://link"/>';
$xml  = simplexml_load_string($html);
$attr = $xml->attributes();

使用dom

$dom = new DOMDocument;
$dom->loadHTML($html);
$nodes = $dom->getElementsByTagName('link');
$attr  = $nodes->item(0)->getAttribute('href');