$re = '/^[1-9]\d{8}(?:,[1-9]\d{8})+$/m';
$str = '923456789
123456789,923456789
123456789,923456789,923456489
,923456789
,92345678
9234567d3
023456789,923456789
723456789,92345678,333333';
preg_match_all($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