title: Square brackets and -x in crontab
body: <p>I'm trying to add a new entry into crontab, the issue I have is that all other entries are written like so:</p>
  
  <pre><code>0 0 * * * [ -x /home/test/test_reports/nightly ] &amp;&amp; /home/test/test_reports/nightly
  </code></pre>
  
  <p>What is the purpose of <code>[ -x /home/test/test_reports/nightly ]</code>?</p>
  
  <p>I tried to Google it but with no luck..</p>