如何在文件未知的情况下查找文件并在PHP中获取文件？

How can I find a file when it's ext unknown and get his ext in PHP?

I wrote this code but its not working (the if returns false)... Thanks.

$pos_ext = array('jpeg', 'jpg', 'gif', 'png', 'tif', 'svg', 'bmp');



            while($row = mysql_fetch_assoc($result))  
            {   


            for ($i = 0 ; $i <= 6 ; ++$i)
            {
                $file_name = "/" . $row['ID'] . "/headerpic." . $pos_ext[$i];
                if (file_exists($file_name)) 
                {
                    $ext = $pos_ext[$i];
                }


            }