Only copy mp3 if it does not exist

mk-usb-music-disk-for-car

@@ -50,9 +50,11 @@ ARTISTS.lines.each do |artist|
     puts "Creating #{dest}"
     FileUtils.mkdir_p(dest)
     mp3_files.each do |mp3_file|
+      unless File.exist?("#{dest}/#{File.basename(mp3_file)}")
         puts "Copying #{mp3_file} -> #{dest}"
         FileUtils.cp(mp3_file, dest)
         system("sync", DEST)
       end
     end
   end
+end