a.rb

require 'fog'
conn = Fog::Storage.new(:provider => 'AWS')
conn.get_bucket("doors-and-dots").body["Contents"].each do |h|
  key = h["Key"]
  if key.match /square100\.[a-z]+$/ 
    puts "processing #{key}"
    obj = conn.get_object("doors-and-dots", key)
    newkey = key.gsub /square100/, 'square200'
    conn.put_object("doors-and-dots", newkey, obj.body, {"x-amz-acl"=>"public-read", "Content-Type"=>"image/jpeg"})
  end
end

doors-and-dots bucket에 있는 square100을 square200 이름으로 복사.