title: How to use environment variables in docker-compose?
body: <p>I would like to be able to use env variables inside docker-compose.yml, with values passed in at the time of <code>docker-compose up</code>. This is the example.</p>
  <p>I am doing this today with basic docker run command, which is wrapped around my own script.
  Is there a way to achieve it with compose, without any such bash wrappers?</p>
  <pre class="lang-yaml prettyprint-override"><code>proxy:
    hostname: $hostname
    volumes:
      - /mnt/data/logs/$hostname:/logs
      - /mnt/data/$hostname:/data
  </code></pre>