$re = '/^(\d+(,\d+)*)$/m';
$str = '# Inválido
,12312.*
123,12312,,12312312
asdasd,123123,12312
1,3123,asadas,123123
12312,12312312,312312,1,3,
,abc,321
# Válido
12312,12312312,312312,1,3
1,2,3
999,999';
preg_match_all($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