title: How can I delete files in a directory which are copied from another directory?
body: <p>I have two directories, say, A and B. A has several files: a1, a2, a3. B also has several files: b1, b2.
  First, I use the following ant tasks to copy all the files from B to A. </p>
  
  <pre><code>&lt;copy todir="A" verbose="true"&gt;
      &lt;fileset dir="B" includes="*"/&gt;
  &lt;/copy&gt;
  </code></pre>
  
  <p>Then I want to undo the steps, i.e. delete the files in A which are copied from B, namely b1 and b2. How can I achieve the goals?</p>
  
  <p>NOTE: the file names in the example are just used for us to understand the problem. I do not know the exact file names in the two directories.</p>