Move up on folder from absolute path

Question

How do I accomplish to move up one folder from absolute path?

File structure:

/folder/
/folder/config.php
/folder/classes/test.php

From test.php I want to include_once or require_once the config.php -file.

I've tried this in test.php, but it doesn't work:

require_once(dirname(__FILE__) . '/../config.php');

Error message: *PHP Fatal error: require_once(): Failed opening required '/loooong-path/classes/../test.php'*

Answer 1

you could try:

require_once(realpath(__DIR__ . '/../config.php'));

Not tested but in theory it is supposed to work.