$re = '/^(?!.*\S[MG]O\b)[a-zA-Z0-9,()]+(?: [a-zA-Z0-9,()]+)*$/mi';
$str = 'aaaa test
test MO test
test this is GO
GO
MO
test AMO test
test AGO test
a
It is 40 GO
It is 40GO
It is 40 GO';
preg_match_all($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