calling include from an included file

The include path is relative to the first file in the include chain.

A good way to ensure the correct include path is to always include from the document root.

This is done like this:

include $_SERVER['DOCUMENT_ROOT'] . '/folder1/folder2/includetwo.php';

The "relative include path" is not shifted to the included file... Which means that using relative paths generally ends badly.

A better solution, that I use almost all the time, is to always work with absolute paths -- and you can mix relatives and absolute paths using __DIR__, to get the directory that contains the file where this is written.

For example, in include_one.php, you'd use :

require_once __DIR__ . '/include_two.php';

To include the include_two.php file that's in the same directory as include_one.php.

And, in main_file.php, you'd use :

require_once __DIR__ . '/../include_one.php';

To include the include_one.php file that's one directory up.

With that, your includes will work, no matter from which file they are called.