title: Extract IDs from CSS
body: <p>I've the CSS file with many entry like</p>
  
  <pre><code>#id1, #id2, #id3, #id4 { ... }
  #id3, #id2 { ... }
  #id2, #id4 { ... }
  </code></pre>
  
  <p>I want to extract list of unique IDs using command line tools (msys).
  Unique means any entry in list presented only once. How?</p>
  
  <p>PS: I know how doing it using python, but what about awk/sed/cat?</p>