codice:
<?php
$dir = "cartella/";

if (is_dir($dir)) 
{
   if ($handler = opendir($dir)) 
     {
     while (($file = readdir($handler)) !== false) 
     {
             $ext = strtolower(end(explode('.', $file)));

             if($ext == "txt")
             {
                echo $file."
";
             }
       }
       closedir($handler);
   }
}

?>