include - PHP require file from top directory

Question

I have several subdomains contained in their own directory above my root site, and an assets folder in my root directory. For example:

/
/assets/
/forums/
/blog/

I'm trying to require() files on php pages in both the root directory, and the subdirectories, for example, assets/include/form.php is required() in both index.php in the root directory and index.php in the forums directory. However, inside form.php, is another require, trying to get another file contained in the include directory.

I can't seem to find a way to require a file inside this form.php where it will work on both the root directory's index.php and the forum directory's index.php.

Is there any way I can explicitly require a file starting from the root directory?

Answer 1

There are several ways to achieve this.

Use relative path from form.php

require_once __DIR__ . '/otherfile.php';

If you're using PHP 5.2 or older, you can use dirname(__FILE__) instead of __DIR__. Read more about magic constants here.

Use the $_SERVER['DOCUMENT_ROOT'] variable

This is the absolute path to your document root: /var/www/example.org/ or C:wampwww on Windows.

The document root is the folder where your root level files are: http://example.org/index.php would be in $_SERVER['DOCUMENT_ROOT'] . '/index.php'

Usage: require_once $_SERVER['DOCUMENT_ROOT'] . '/include/otherfile.php';

Use an autoloader

This will probably be a bit overkill for your application if it's very simple.

Set up PHP's include paths

You can also set the directories where PHP will look for the files when you use require() or include(). Check out set_include_path() here.

Usage: require_once 'otherfile.php';

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Note:

I see some answers suggest using the URL inside a require(). I would not suggest this as the PHP file would be parsed before it's included. This is okay for HTML files or PHP scripts which output HTML, but if you only have a class definition there, you would get a blank result.