title: Check if referrer exists
body: <p>In my code, I want to check if a referrer url exists and if the referrer url contains a specific sub string.  I know how to check for the sub string:</p>
  
  <pre><code>If( InStr( Request.UrlReferrer.ToString(), "some sub string here" ) &gt; 0 ) Then
  </code></pre>
  
  <p>But I don't know how to check if a referrer exists or not.  No refer exists if the url is entered in manually in the address bar.  So I tried this, but this does not work:</p>
  
  <pre><code>If (Not (Request.UrlReferrer.ToString() = "")) And (InStr(Request.UrlReferrer.ToString(), "some sub string here") &gt; 0) Then
  </code></pre>
  
  <p>Anyone know how do check if a referrer exists?</p>