title: Checking for null string in bash
body: <p>Is there any difference between the following tests?</p>
  
  <pre><code>[[ "$STRING" = "" ]] &amp;&amp; exit 1;
  
  
  [[ "x$STRING" = "x" ]] &amp;&amp; exit 1;
  
  
  [[ -z $STRING ]] &amp;&amp; exit 1;
  </code></pre>