ho capito qual e' la differenza
Let us create one PHP file and name it as data.php . Here is the content of this file

<?
echo "Hello
"; // this will print Hello with one line break
?>

Now let us create one more file and from that we will be including the above data.php file . The name of the file will be inc.php and the code is given below.

<?
include "data.php"; // this will display Hello once
include "data.php"; // this will display Hello once
include "data.php"; // this will display Hello once

include_once "data.php"; // this will not display as the file is already included.
include_once "data.php"; // this will also not display as the file is already included.
?>