//download.php

<?php
   $data = "1,2,3,4,5,6,7,8";
   
   $file = "file.csv";

   header('Pragma: anytextexeptno-cache', true);
   header('Content-type: application/force-download');
   header('Content-Transfer-Encoding: Binary');
   header('Content-disposition: attachment;
   filename='.basename($file));
   echo $data;   

?>