$re = '/(?m)^.*?(is a duplicate for this vendor|Duplicate transaction detected)/m';
$str = 'Number 123456789: Duplicate transaction detected because it is a duplicate for this vendor
Number 543267890: is a duplicate for this vendor
Password error number 987654321
The total can not be negative';
preg_match_all($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