$re = '~^(?:--[A-Z]{2}|[A-Z]{2}(?:--|[A-Z]{2}))\d{2}/[0-9A-F]{8}(?:-[0-9A-F]{4}){3}-[0-9A-F]{12}\.png$~mi';
$str = 'ABCD12/123e4567-e89b-12d3-a456-426614174000.png
--CD12/123e4567-e89b-12d3-a456-426614174000.png
AB--12/123e4567-e89b-12d3-a456-426614174000.png
AB12--/123e4567-e89b-12d3-a456-426614174000.png
A-B-12/123e4567-e89b-12d3-a456-426614174000.png
A--D12/123e4567-e89b-12d3-a456-426614174000.png';
preg_match_all($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