title: What is the correct way to join multiple path components into a single complete path in emacs lisp?
body: <p>Suppose I have variables <code>dir</code> and <code>file</code> containing strings representing a directory and a filename, respectively . What is the proper way in emacs lisp to join them into a full path to the file?</p>
  
  <p>For example, if <code>dir</code> is <code>"/usr/bin"</code> and <code>file</code> is <code>"ls"</code>, then I want <code>"/usr/bin/ls"</code>. But if instead <code>dir</code> is <code>"/usr/bin/"</code>, I still want the same thing, with no repeated slash.</p>