title: Using grep and ls -a commands
body: <p>Using an <code>ls –a</code> and <code>grep</code>, how would you list the name of all of the files in /usr starting with the letter p or the letter r or the letter s using a single grep command? </p>
  
  <p>would this be right?</p>
  
  <pre><code>ls –a | grep [prs] /usr
  </code></pre>