title: Purpose of square brackets in shell scripts
body: <p>I came across this line in one of the shell scripts:</p>
  <pre><code>[-f $host_something ] &amp;&amp; .$host_something
  </code></pre>
  <p>What are the square brackets with the <code>-f</code> switch supposed to do, and what is the point of ANDing it with the same environment variable?</p>