title: Best method to find duplicate of a particular file or a particular set of files
body: <p>I have been using <code>fdupes</code> to find duplicate files in my filesystem, however, I often find myself wanting to, either, find duplicates of <em>a particular file</em> or find duplicates of the files in a particular directory.</p>
  
  <p>To elaborate, if I call</p>
  
  <pre><code>fdupes dir1 dir2
  </code></pre>
  
  <p>The result will be all duplicate files found in the collected set of files in <code>dir1</code> and <code>dir2</code>.  However, I would really like to be able to do something like</p>
  
  <pre><code>fdupes-alternative file dir
  </code></pre>
  
  <p>to find duplicates of <code>file</code> in <code>dir</code> without being bothered with duplicate files in <code>dir</code>.  Or even being able to something like</p>
  
  <pre><code>fdupes-alternative dir1 dir2
  </code></pre>
  
  <p>and to check of any of the files in <code>dir1</code> are duplicated in <code>dir2</code>, again, ignoring the duplicates if they are either all in <code>dir1</code> or <code>dir2</code>.</p>
  
  <p>Are there any tools which does this sort of thing, or any easy way to do this kind of thing?</p>