title: Inspect stdout from the middle of chained apps
body: <p>Consider this example chain:</p>
  
  <pre><code>cat foo.txt | grep -v foo | grep -v bar | grep -v baz
  </code></pre>
  
  <p>I'd like to inspect the contents stdout of the second grep as well as the resulting stdout:</p>
  
  <pre><code>cat foo.txt | grep -v foo | grep -v bar | UNKNOWN | grep -v baz
  </code></pre>
  
  <p>So I need a tool, UNKNOWN, that for instance dumps the contents of stdout to a file and also passes stdout along the chain.</p>
  
  <p>Does the tool, UNKNOWN, exists (both Windows and Linux answers are relevant) ?</p>