$re = '/(.*)<a[^=]*="[^\/]*\/([^\/]+\/)*(.*)">.*/m';
$str = '<!-- wikibase-toolbar --><span class="wikibase-toolbar-container"><span class="wikibase-toolbar-item wikibase-toolbar ">[<span class="wikibase-toolbar-item wikibase-toolbar-button wikibase-toolbar-button-edit"><a href="/wiki/Special:SetSiteLink/Q170596">edit</a></span>]</span></span>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php