$re = '/\[\d+(?:,\d+)+]/m';
$str = '[,][123,1][,][456,2][,][789,3][,][,][,][,][,][,][,][,]
[123]
[123,1,2,34]
[123,1,2]
[]
[1,,2]
[,1,2]';
preg_match_all($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