update_s3_content_type.rb

require 'aws'
require 'mime/types'

access_key_id = ENV['AWS_ACCESS_KEY_ID']
secret_access_key = ENV['AWS_SECRET_ACCESS_KEY']
bucket_name = ENV['S3_BUCKET']

s3 = AWS::S3.new(
  :access_key_id => access_key_id,
  :secret_access_key => secret_access_key
)
bucket = s3.buckets[bucket_name]
bucket.objects.each do |object|
        next unless object.key.include? '.'
        print object.key
        filename = File.basename(object.key)
        mime_type = MIME::Types.type_for(filename).first.to_s
        if mime_type.empty?
                puts " - no type found!"
        else
                puts " - type #{mime_type}"
                object.copy_from(object.key, { :content_type => mime_type })
        end
end