$re = '/_thumb(@[2-3]x)?\.jpg/';
$str = 'grwior_thumb.jpg
grwior.jpg
vuoetrjrt_thumb@2x.jpg
vuoetrjrt.jpg
hafiruwhf_thumb.jpg
hafiruwhf_thumb@2x.jpg
hafiruwhf_thumb@3x.jpg
hafiruwhf.jpg
';
preg_match_all($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