For downloading assets (in this case Paperclip attachments) from S3 to local filesystem

download-from-s3.rb

require 'aws/s3'

AWS::S3::Base.establish_connection!(
  :access_key_id     => 'id',
  :secret_access_key => 'secret'
)

missing_uploads = [1,2,3,4] # ID's from the attachments you want to download

log = File.open('file-import-log.txt','w')

bucket = AWS::S3::Bucket.find('bucket-name'); nil
missing_uploads.each do |id|
  bucket.objects(:prefix => "assets/#{id}/").each do |o|    
    `mkdir -p #{File.dirname(o.key)}`
    open(o.key, 'w') do  |file|
      AWS::S3::S3Object.stream(o.key, o.bucket.name) do |chunk|
        file.write chunk
      end
    end
  end
  log.write "#{Time.now} Downloaded asset #{id}\n"
end