title: Variable inside a square bracket in Bash
body: <p>What does it mean to have a variable inside square brackets? Boolean?</p>
  
  <p>For example:</p>
  
  <ol>
  <li><code>[ $FILES ] || { print "File not found." }</code></li>
  <li><code>[ $VERIFY ] &amp;&amp; { print "file verification fail" }</code></li>
  </ol>