title: lex generates no output
body: <p>Just following the tutorial at <a href="https://begriffs.com/posts/2021-11-28-practical-parsing.html" rel="nofollow noreferrer">https://begriffs.com/posts/2021-11-28-practical-parsing.html</a>. My .l file looks like:</p>
  <pre><code>/* catcot.l */
  
  %{
  #include &lt;stdio.h&gt;
  %}
  
  %%
  
  cot { printf(&quot;portable bed&quot;); }
  cat { printf(&quot;thankless pet&quot;); }
  cats { printf(&quot;anti-herd&quot;); }
  </code></pre>
  <p>I give the command:</p>
  <pre><code>lex catcot.l
  </code></pre>
  <p>And the generated output is empty:</p>
  <pre><code>$ ls -l
  total 16
  -rw-r--r--  1 falk  staff  141 Dec 27 14:19 catcot.l
  -rw-r--r--  1 falk  staff    0 Dec 27 14:19 lex.yy.c
  </code></pre>
  <p>Running with -v shows that lex is really running (<code>flex version 2.5.35 Apple(flex-32)</code>) and introducing errors in the code gives the expected error messages, but no output ever gets generated.</p>