gistfile1.rb

# Install kicker on osx: sudo gem install kicker --source http://gemcutter.org\
#
# Place a `.kick' file with this code in the root of your project, which contains the file to watch.
# Then start running kicker from the project root: $ kicker

FILE_TO_WATCH = 'mockup-1.psd'

counter = nil

if File.exist?('output')
  last = Dir.glob("output/*.png").sort.last
  if last =~ /mockup-(\d+)\.png$/
    counter = $1.to_i
  else
    counter = 0
  end
else
  FileUtils.mkdir_p 'output'
  counter = 0
end

process do |files|
  if files.delete(FILE_TO_WATCH)
    counter += 1
    execute "sips #{FILE_TO_WATCH} -s format png --out output/mockup-#{counter}.png"
  end
end