title: docker entrypoint : use env variables in a required format
body: <pre><code>ARG PORT=8004
  #start server
  EXPOSE ${PORT}
  
  ENTRYPOINT [ &quot;gunicorn&quot;, &quot;-w&quot;, &quot;4&quot;, &quot;-b&quot;, &quot;0.0.0.0:8004&quot;,&quot;wsgi:app&quot; ]
  </code></pre>
  <p>I need to use the PORT  to specify it as &quot;0.0.0.0:8004&quot;</p>
  <p>what are all the ways I can use PORT=8004 in the following format
  &quot;0.0.0.0:8004&quot;</p>
  <p>I have been trying</p>
  <pre><code>ARG PORT=8004
  ENV PORT=$PORT
  #start server
  EXPOSE ${PORT}
  ENTRYPOINT [ &quot;gunicorn&quot;, &quot;-w&quot;, &quot;4&quot;, &quot;-b&quot;, &quot;0.0.0.0:${PORT}&quot;,&quot;wsgi:app&quot; ]
  </code></pre>
  <p>but I am getting Error: '${PORT}' is not a valid port number.</p>