s3_copy_bucket.rb

module AWS
  module S3
    class Bucket
      def copy_to(target)
        each do |obj|
          returning Base.put("/#{target}/#{obj.key}", { 'x-amz-copy-source' => "/#{name}/#{obj.key}", 'x-amz-metadata-directive' => 'COPY', 'Content-Length' => 0 }) do
            S3Object.acl(obj.key, target, S3Object.acl(obj.key, name))
          end
        end
      end
    end
  end
end

use_s3_copy_bucket.rb

require 'aws/s3'
require 's3_copy_bucket'
AWS::S3::Base.establish_connection! :access_key_id => 'foo', :secret_access_key => 'bar'
src = AWS::S3::Bucket.find('my.source.bucket')
dest = AWS::S3::Bucket.find('my.destination.bucket')
src.copy_to(dest.name)