PHP Dynamic include based on current file path

I think you need to use __FILE__ (it has two underscores at the start and at the end of the name) and DIRECTORY_SEPARATOR constants for working with files based on the current file path.

For example:

<?php
  // in this var you will get the absolute file path of the current file
  $current_file_path = dirname(__FILE__);
  // with the next line we will include the 'somefile.php'
  // which based in the upper directory to the current path
  include(dirname(__FILE__) . DIRECTORY_SEPARATOR . '..' . DIRECTORY_SEPARATOR . 'somefile.php');

Using DIRECTORY_SEPARATOR constant is more safe than using "/" (or "\") symbols, because Windows and *nix directory separators are different and your interpretator will use proper value on the different platforms.

You can place your includes inside conditional logic.

<?php   
if (isset($_GET['service'])) {
    include('subContent/serviceMenu.html');
} else if (isset($_GET['business'])) {
    include('subContent/business_menu.html');
} else if (isset($_GET['info'])) {
    include('subContent/info_menu.html');
}
else {
    include('subContent/banner.html');
}
?>
<a href="http://localhost/yourpage.php?service" />