$re = '/<span class=\"select\"[\w\d\s\"=]*><a href=[\w\d\s\"<>:/.-]+</a></span>/m';
$str = '<span class="select" foo="1"><a href="https://www.domain.tld">Word 1</a></span><span class="select"><a href="https://www.domain.tld">Word 2</a></span><span class="no_select"><a href="https://www.domain.tld">Word 3</a></span><span class="select" bar="2"><a href="https://www.domain.tld">Word 4</a></span>';
preg_match_all($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