$re = '/<a.*?<\/a>|http:\/\/\S+/';
$str = 'adasdas http://www.stackoverflow.com asdasas
adasdasahttp://www.stackoverflow.com/something asdas
adasdas<a href="somelink"> http://www.stackoverflow.com </a>asdasas
adasdasa<a href="somelink">http://www.stackoverflow.com/something</a> asdas';
preg_match_all($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