Optimizes a whole folder using zopflipng as fish script (just copy paste into the fish shell)

zopflipng_folder.fish

for file in *.png
      echo -n "Optimizing $file..."
      if zopflipng -y -m $file (basename $file .png)".min.png" | grep "Result is smaller"
          mv (basename $file .png)".min.png" $file
          echo " optimized."
      else
          rm (basename $file .png)".min.png"
          echo
      end
  end