Passing a variable from one php document to another

Passing a variable from one php document to another

I have this PHP code:
poster.php:
<?php
$field_password = 1;
if (empty($_POST['password'])) {
$field_password = 0;
}
?>
I want the "$field_password" variable passed to another page that is
called register.php without using code like this:
include 'poster.php';
required_once 'poster.php';
And so on, I only need the $field_password variable passed. Any ideas how
to do that? oh and btw, the more secure it is, the better.