$re = '/^-?(?:[1-9][0-9]*(?:,[0-9]+)?|[1-9][0-9]{1,2}(?:,[0-9]{3})+)$/m';
$str = '123,456,789
-12,34
1234
-8
1,2,345
';
preg_match_all($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