title: How to check which Emacs I am using?
body: <p>I have two Emacs (Aquamacs and text-based Emacs) on my Mac.</p>
  <p>In my <code>.emacs</code> file, I can check if I'm using Aquamacs with ...</p>
  <pre><code>(boundp 'aquamacs-version)
  </code></pre>
  <p>How can I check if I'm using text based emacs?</p>
  <h2>EDIT</h2>
  <p>Jürgen Hötzel's answer works, but for text based emacs, using</p>
  <pre><code>(unless (null window-system) ...) 
  </code></pre>
  <p>is better as <code>(window-system)</code> is not defined.</p>