Simple PHP Post-Redirect-Get code example

Simplest scenario:

if ($_POST) {
   // Execute code (such as database updates) here.

   // Redirect to this page.
   header( "Location: {$_SERVER['REQUEST_URI']}", true, 303 );
   exit();
}

Use REQUEST_URI. Do not use PHP_SELF as in most CMS systems and frameworks PHP_SELF would refer to /index.php.

A snippet of code:

if (count($_POST)) {
    // process the POST data
    // your code here- so for example to log a user in, register a new account..
    // ...make a payment...etc

    // redirect to the same page without the POST data, including any GET info you
    // want, you could add a clause to detect whether processing the post data has 
    // been successful or not, depending on your needs

    $get_info = "?status=success";

    // if not using rewrite
    // header("Location: ".$_SERVER['PHP_SELF'].$get_info);

    // if using apache rewrite
    header("Location: ".$_SERVER['REQUEST_URI'].$get_info);
    exit();
}

    Browser
   HTML form
  method=POST
       |
       v
    PHP app
  reads $_POST
sends 303 header
       |
       v
    Browser
receives header
 redirected to
   new page
       |
       v
    PHP app
  reads $_GET
 does whatever

A common use is in login authentication. That's the process flow when user submits the login form. PHP app authenticates user via $_POST vars. Sends a 303 header back to browser when the user has successfully authenticated. So user is redirected to a new page.