$re = '/Error importing row no\. (\d+):/';
$str = '2012-15-08 07:04 Bla bla bla blup
2012-15-08 07:05 *** Error importing row no. 5: The import of this line failed because bla bla
2012-15-08 07:05 Another text that I don\'t want to search...
2012-15-08 07:06 Another text that I don\'t want to search...
2012-15-08 07:06 *** Error importing row no. 5: The import of this line failed because bla bla
2012-15-08 07:07 Import has finished bla bla';
preg_match_all($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