title: Variable assignment withing .env file
body: <p>I have one .env file , that looks like :</p>
  
  <pre><code>NODE_ENV = local
  PORT = 4220
  BASE_URL = "http://198.**.**.**:4220/"
  
  PROFILE_UPLOAD = http://198.**.**.**:4220/uploads/profile/
  POST_UPLOAD = http://198.**.**.**:4220/uploads/discussion/
  COMPANY_UPLOAD = http://198.**.**.**:4220/uploads/company/
  ITEM_UPLOAD  = http://198.**.**.**/uploads/item/
  GROUP_UPLOAD  = http://198.**.**.**/uploads/group/
  </code></pre>
  
  <p>I want to do something like this :</p>
  
  <pre><code>NODE_ENV = local
  IP = 198.**.**.**
  PORT = 5000
  BASE_URL = http://$IP:$PORT/
  
  PROFILE_UPLOAD = $BASE_URL/uploads/profile/
  POST_UPLOAD = $BASE_URL/uploads/discussion/
  COMPANY_UPLOAD = $BASE_URL/uploads/company/
  ITEM_UPLOAD  = $BASE_URL/uploads/item/
  GROUP_UPLOAD  = $BASE_URL/uploads/group/
  </code></pre>
  
  <p>Expected result of <code>BASE_URL</code> is <code>http://198.**.**.**:4220/</code></p>
  
  <p>I have tried many few syntax but not getting computed values</p>
  
  <p>Tried Syntax : <code>"${IP}"</code> ,  <code>${IP}</code> ,  <code>$IP</code></p>
  
  <p>I have used <strong><a href="https://www.npmjs.com/package/dotenv" rel="noreferrer">dotenv</a></strong> package , for accessing env variables.</p>