title: How nodejs reads and writes .env files？
body: <p>How to read and write env files?</p>
  <p>Original file：</p>
  <pre><code># I am a note ...
  key1=value1
  
  key2=value2
     # I am a note ...
  </code></pre>
  <p>I need a function <code>setEnv(key, value)</code>.</p>
  <p>run <code>setEnv('key1', 'value2')</code>， Let it become：</p>
  <pre><code># I am a note ...
  key1=value2
  
  key2=value2
     # I am a note ...
  </code></pre>
  <p>How can I achieve it?</p>