title: How to add dynamic file to docker container
body: <p>whenever I run a docker container, I want to send dynamic filename as some environment variable.</p>
  
  <p>That is accessible in container so its printing its value when we 'echo'.</p>
  
  <p>But ADD command not adding that file.</p>
  
  <p>Dockerfile:</p>
  
  <pre><code>ADD $filename ./
  echo ls # Not showing file
  </code></pre>
  
  <p>docker run -e filename='/path/to/file.extension'  </p>