title: iterate over stdin fish (context: filter music files by genre grep)
body: <p>I have this:</p>
  
  <pre><code>for file in **/*.ogg;  
      if ffprobe "$file" 2&gt;&amp;1 | sed -E -n 's/^ *GENRE *: (.*)/\1/p' | grep -q "$argv"; 
          echo "$file"
      else
      end
  end
  </code></pre>
  
  <p>but I would like to turn it into a function which will take a list of filenames as standard-input:</p>
  
  <pre><code>$ find . -maxdepth 1 -not -type d -exec du -h {} + | cut -f2 | filterByGenre Classical
  </code></pre>