title: attempt to call field 'read' (a nil value)
body: <p>I'm playing with Lua following the link: <a href="https://www.lua.org/pil/4.3.3.html" rel="nofollow noreferrer">https://www.lua.org/pil/4.3.3.html</a>. Now I was confused with the use of 'read' in the code. </p>
  
  <pre><code>&gt; repeat
  line=os.read()
  until line ~=""
  stdin:2: attempt to call field 'read' (a nil value)
  stack traceback:
      stdin:2: in main chunk
      [C]: in ?
  </code></pre>
  
  <p>Any comments are greatly appreciated.  </p>