How do I include a file over 2 directories back?

Question

.. selects the parent directory from the current. Of course, this can be chained:

../../index.php

This would be two directories up.

To include a file one directory back, use '../file'. For two directories back, use '../../file'. And so on.

Although, realistically you shouldn't be performing includes relative to the current directory. What if you wanted to move that file? All of the links would break. A way to ensure that you can still link to other files, while retaining those links if you move your file, is:

require_once($_SERVER['DOCUMENT_ROOT'] . 'directory/directory/file');

DOCUMENT_ROOT is a server variable that represents the base directory that your code is located within.

. = current directory
.. = parent directory

So ../ gets you one directory back not two.

Chain ../ as many times as necessary to go up 2 or more levels.

include dirname(__FILE__).'/../../index.php';

is your best bet here, and it will avoid most of the relative path bugs you can encounter with other solutions.

Indeed, it will force the include to always be relative to the position of the current script where this code is placed (which location is most likely stable, since you define the architecture of your application). This is different from just doing include '../../index.php' which will include relatively to the executing (also named "calling") script and then relatively to the current working directory, which will point to the parent script that includes your script, instead of resolving from your included script's path.

From the PHP documentation:

Files are included based on the file path given or, if none is given, the include_path specified. If the file isn't found in the include_path, include will finally check in the calling script's own directory and the current working directory before failing.

And the oldest post I've found citing this trick dates back to 2003, by Tapken.

You can test with the following setup:

Create a layout like this:

htdocs
¦   parent.php
¦   goal.php
¦
+---sub
    ¦   included.php
    ¦   goal.php

In parent.php, put:

<?php
include dirname(__FILE__).'/sub/included.php';
?>

In sub/included.php, put:

<?php
print("WRONG : " . realpath('goal.php'));
print("GOOD : " . realpath(dirname(__FILE__).'/goal.php'));
?>

Result when accessing parent.php:

WRONG : X:\htdocs\goal.php
GOOD : X:\htdocs\sub\goal.php

As we can see, in the first case, the path is resolved from the calling script parent.php, while by using the dirname(__FILE__).'/path' trick, the include is done from the script included.php where the code is placed in.

Beware, the following NOT equivalent to the trick above contrary to what can be read elsewhere:

include '/../../index.php';

Indeed, prepending / will work, but it will resolve just like include ../../index.php from the calling script (the difference is that include_path won't be looked afterwards if it fails). From PHP doc:

If a path is defined — whether absolute (starting with a drive letter or \ on Windows, or / on Unix/Linux systems) or relative to the current directory (starting with . or ..) — the include_path will be ignored altogether.