How do I safely get the internal path to the current site in a multisite setup?
You can use conf_path to get the path root to the current site - then append the rest of your path to that.


  Returns the configuration path based on the site's hostname, port, and
  pathname.


e.g:

$apple_icon =  array(
  '#tag' =&gt; 'link',
  '#attributes' =&gt; array(
    'href' =&gt; base_path() . conf_path() . '/apple-touch-icon.png',
    'rel' =&gt; 'apple-touch-icon',
  ),
);
drupal_add_html_head($apple_icon, 'apple-touch-icon');