a.php:

$etc = 'LOTS OF TEXT'



index.php?k=etc:

<?php
require("a.php");
require("vars_and_funcs.php");
get_index_text();
?>



vars_and_funcs.php:

function get_index_text()
{
$foo = htmlentities($_GET["k"]);
echo $foo;
echo ${$foo};
}