$re = '/(?<=\d\.\s)(?:(?!\s-\s|\d\.\s).)+/m';
$str = ' 3. product - sub product. The regex gives me the product (first part). However, there are some product which does not have sub product. For example. 6. ComprehensiveBolt. The regex 3. product - sub product
6. ComprehensiveBolt';
preg_match_all($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