Every HTTP request received by a Slim application will have a root URI and a resource URI.

Root URI

The root URI is the physical URL path of the directory in which the Slim application is instantiated and run. If a Slim application is instantiated in index.php within the top-most directory of the virtual host’s document root, the root URI will be an empty string. If a Slim application is instantiated and run in index.php within a physical subdirectory of the virtual host’s document root, the root URI will be the path to that subdirectory with a leading slash and without a trailing slash.

Resource URI

The resource URI is the virtual URI path of an application resource. The resource URI will be matched to the Slim application’s routes.

Assume the Slim application is installed in a physical subdirectory /foo beneath your virtual host’s document root. Also assume the full HTTP request URL (what you’d see in the browser location bar) is /foo/books/1. The root URI is /foo (the path to the physical directory in which the Slim application is instantiated) and the resource URI is /books/1 (the path to the application resource).

You can get the HTTP request’s root URI and resource URI with the request object's getRootUri() and getResourceUri() methods:

<?php
$app = new \Slim\Slim();

// Get request object
$req = $app->request;

//Get root URI
$rootUri = $req->getRootUri();

//Get resource URI
$resourceUri = $req->getResourceUri();