sipsで画像のコピー&リサイズ。@2x.png

resize.rb

require 'pp'
require 'pathname'

resize_command = 'sips -z 34 34 --out out/%2$s %1$s'
copy_command = 'cp %s out/%s'

Pathname.glob('./*').sort.each_with_index do |path, idx|
  next unless path.to_s.match(/png$/)
  system(copy_command % [path.to_s, idx.to_s+'@2x.png'])
  system(resize_command % [path.to_s, idx.to_s+'.png'])
end