title: How to set docker env file that inside the image
body: <p>i am a totally docker newb, so sorry for that</p>
  
  <p>i have stand-alone docker image (some node app),
  that i want to run in different environments.</p>
  
  <p>i want to set up the env file with <code>run RUN --env-file &lt;path&gt;</code>
  How ever, i want to use the env files that inside the image (so i can use different files per env),
  and not on server.
  so  would be the path inside image. </p>
  
  <p>is there any way to do so? 
  perhaps like "cp" (<code>docker cp [OPTIONS] CONTAINER:&lt;path&gt;</code>)
  but doesn't seem to work.</p>
  
  <p>what the best practice here?
  am i making sense?
  Thanks!! </p>