title: How can I reference an environment variable from Node's .env file?
body: <p>I have manually defined an environment variable in the shell, and I want to be able to reference this environment variable in a <code>.env</code> file in Node. Node's <code>.env</code> files don't seem to be able to support calling existing environment variables.</p>
  <p>Example <code>.env</code></p>
  <pre><code>testfilepath=$TEST_PATH/testfile
  </code></pre>
  <p>Error:</p>
  <pre><code>npm start
  Error: File does not exist at path: $TEST_PATH/testfile.
  </code></pre>
  <p>How can I reference an existing environment variable in a Node .env file?</p>