title: Docker: how to get back to initial directory after issuing a WORKDIR command
body: <p>There is no explanation in docker doc or seemingly any builtin variable in docker to find the original working directory where the image is being built. 
  I want to run commands on different directories and at some point get back to where i launched docker build from.
  Am I missing something obvious?
  Thanks.</p>
  
  <p>Dockerfile example:</p>
  
  <pre><code>FROM ubuntu
  WORKDIR /my_folder
  RUN command1
  WORKDIR ??? // How do i get back to the Dockerfile folder?
  RUN command2
  </code></pre>