Get parent directory of running script

In PHP, what would be the cleanest way to get the parent directory of the current running script relative to the www root? Assume I have:

$_SERVER['SCRIPT_NAME'] == '/relative/path/to/script/index.php'

Or just:

$something_else == '/relative/path/to/script/'

And I need to get /relative/path/to/ with slashes properly inserted. What would you suggest? A one liner is preferred.

EDIT

I need to get a path relative to the www root, dirname(__FILE__) gives me an absolute path in the filesystem so that won’t work. $_SERVER['SCRIPT_NAME'] on the other hand ‘starts’ at the www root.

Answer

If your script is located in /var/www/dir/index.php then the following would return:

dirname(__FILE__); // /var/www/dir

or

dirname( dirname(__FILE__) ); // /var/www

---

Edit

This is a technique used in many frameworks to determine relative paths from the app_root.

File structure:

 /var/
      www/
          index.php
          subdir/
                 library.php

index.php is my dispatcher/boostrap file that all requests are routed to:

define(ROOT_PATH, dirname(__FILE__) ); // /var/www

library.php is some file located an extra directory down and I need to determine the path relative to the app root (/var/www/).

$path_current = dirname( __FILE__ ); // /var/www/subdir
$path_relative = str_replace(ROOT_PATH, '', $path_current); // /subdir

There’s probably a better way to calculate the relative path then str_replace() but you get the idea.