title: Access $HOME in Dockerfile ENV instruction
body: <p>I'm trying to set an environment variable with ENV instruction dynamically using $HOME variable (i think its a system environment variable).</p>
  <p>But ENV is not able to access $HOME. Its blank. Although i'm able to echo $HOME.</p>
  <pre><code>FROM somebaseimage
  
  ....
  ....
  
  USER 5051
  
  RUN echo $HOME
  # prints /home/myuser
  
  ENV MY_JSON_FILEPATH=&quot;${HOME}/my_file.json&quot;
  
  RUN echo $MY_JSON_FILEPATH
  # prints /my_file.json
  </code></pre>
  <p>I have tried
  &quot;${HOME}/my_file.json&quot;, &quot;$HOME/my_file.json&quot;; both don't work.</p>
  <p>What would be the best way to set such environment variable?</p>