Rake task to find unused images on Rails project to deletion.

find_unused_images.rake

# It requires ACK - http://betterthangrep.com/
task :find_unused_images do
  images = Dir.glob('app/assets/images/**/*')

  images_to_delete = []
  images.each do |image|
    unless File.directory?(image)
      # print "\nChecking #{image}..."
      print "."
      result = `ack -1 -G '(app|public)' --ruby --html --css --js #{File.basename(image)}`
      if result.empty?
        images_to_delete << image
      else
      end
    end
  end
  puts "\n\nDelete unused files running the command below:"
  puts "rm #{images_to_delete.join(" ")}"
end

Here's a clean version using the updated ack command from @danielricecodes:

task :find_unused_images do
  images_to_delete = Dir.glob('app/assets/images/**/*').reject(&File.method(:directory?)).select do |img|
    print '.'
    `ack -g -i '(app|public)' | ack -x -w #{File.basename(img).shellescape}`.empty?
  end

  puts "\n\nDelete unused files running the command below:"
  puts "rm #{images_to_delete.map(&:shellescape).join(' ')}"
end

shellescape

Add the -1 option to continue with the next file if a result was found
ack -g -i '(app|public)' | ack -x -1 -w #{File.basename(img).shellescape}.empty?