php ajax debug method make log in a text file

log into file
//
ob_start();
echo "<pre>";
print_r($data);
echo "</pre>";
$a=ob_get_contents();
//DAL::remove("insert into mytest(vvv) values('$a')");
$filename = "file.txt";
$file = fopen($filename, "w"); //open file
fwrite($file, $a); //first line
fclose($file); //close
ob_end_clean();
//