title: xmlstarlet update value nothing happens
body: <p>I have an xml file</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;preferences&gt;
      &lt;!--General options--&gt;
      &lt;options&gt;
              &lt;dbHost&gt;localhost&lt;/dbHost&gt;
              &lt;dbUser&gt;bwserver&lt;/dbUser&gt;
              &lt;dbPass&gt;bwserver&lt;/dbPass&gt;
              &lt;dbPort&gt;3306&lt;/dbPort&gt;
  </code></pre>
  
  <p>How can i update the value dbUser?</p>
  
  <p>When I type</p>
  
  <pre><code>xmlstarlet edit --update '/preferences/options/dbUser/'  --value 123 preferences.xml
  </code></pre>
  
  <p>nothing happens.  I only see the file contents in terminal. The xml file was not touched.</p>