$re = '/^(?!(?:[^\n\p{Greek}]*\p{Greek}){3})[\p{Latin}\p{Hebrew}\p{Greek}]+$/um';
$str = 'A
b
β
aβ
aaaββג
aaaββגגג
aβaגβaגג
aβaaβגβגג ';
preg_match_all($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