$re = '/^(.*;{1})/m';
$str = '17:25:31;http://example1.com/viewtopic.php?f=8&t=189;example1.com;127.0.0.1 2013-10-19
17:22:32;http://example2.com;example2.com;127.0.0.1 2013-10-19
20:18:28;http://example3.com/threads/example-text-in-url.27304/;example3.com;127.0.0.1 2013-10-19';
preg_match_all($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