How can I find the root directory on the server?

echo $_SERVER['DOCUMENT_ROOT'];

      

        
        
        
      

    

The above line will give you the root directory of your site.

You can define the path directly as a constant somewhere in your shared file including the file

define('PATH_TO_PROJECT_ROOT', '/path/to/projectroot/');

      

        
        
        
      

    

and use constant wherever you want