Assuming you are running under Apache, you can make use of the
$_SERVER["DOCUMENT_ROOT"] variable to get the file path instead of URIs.
Lets take an example...
Assume you have the following directory layout on your Apache HTTP server:
/htdocs
/htdocs/yourwebsite
/htdocs/yourwebsite/inc
/htdocs/yourwebsite/core
Assume in /inc/vars.inc you have the following:
$g_var1 = "hello ";
$g_var2 = "world";
Then in, say, test.php you can do the following:
require_once($_SERVER["DOCUMENT_ROOT"] . "/inc/vars.inc");
echo $g_var1 . $g_var2;
?>