title: grep -r --include not works but --exclude works
body: <p>In bash,</p>
  <pre><code>grep -r --exclude={*.c,} 'HELLO'  // exclude c files
  
  grep -r --include={*.c,} 'HELLO'  // just same with grep -r 'HELLO'
  </code></pre>
  <p>What's the problem?</p>