包含文件的不同路径

I have the following structure of my project (watch image). I need include menu.php in each file but index.php need a different path:

index.php: include('../contenido/menu.php');
agregar.php: include('../../contenido/menu.php');

How can I solve that issue? I do not use a framework.

Set the include path based on the file in question.

You can add a relative path using the __DIR__ magic constant.

For example, in index.php...

set_include_path(implode(PATH_SEPARATOR, [
    __DIR__ . '/../contenido',
    get_include_path()
]));

and in your vistas/productos scripts...

set_include_path(implode(PATH_SEPARATOR, [
    __DIR__ . '/../../contenido',
    get_include_path()
]));

Then, it doesn't matter where you are, you can simply add

include 'menu.html';