$re = '/\b(?:\d{6} \d{5}|[1-9]\d{4} \d{5}|[1-9]\d{9}|\d{11})\b/m';
$str = '1234567890
01234567890
12345 67890
012345 67890
';
preg_match_all($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