title: How do you use grep to find terms that are n characters long?
body: <p>I'm using grep to filter the Mac OS X dictionary words file (by default located at /usr/share/dict/words).</p>
  
  <p>I want to use grep to retrieve all words four characters long. How do I do this?</p>
  
  <p>My best guess for how to do this was:</p>
  
  <pre><code>grep [:alpha:]{4} words
  </code></pre>
  
  <p>But that returns zero results.</p>