Here is a quick ruby file for sending customer info from a db to a list in mailchimp.

mailchimp-adhoc-uploader.rb

#! /usr/bin/env ruby

require 'logger'
require 'net/http'
require 'mysql2'
require 'gibbon'

@log = Logger.new("/mailchimp_sender_log.log", 5, 1024000)
@log.level = Logger::INFO

@myst_db = Mysql2::Client.new(:host => "host", :username => "username", :password => "password")
// add your own db credentials

@log.info("my db connection: #{@myst_db}")

# establish mailchimp connection
api_key = "api-key" // add your own mailchimp api key

@gibbon = Gibbon::API.new(api_key)

@log.info("mailchimp connection ok with api_key: #{api_key}")

@mc_list_id = 'id' // add your own mailchimp list id

referrals = @myst_db.query("SELECT * FROM mind_app_demo.referral_program_mc")

#def subscribe_batch_to_list(batch)
referrals.each_slice(3) do |batch|
  begin
    prepared_batch = batch.map do |referral|
      { 
        :EMAIL => {:email => referral['email']}, 
        :EMAIL_TYPE => 'html', 
        :merge_vars => {
        :MMERGE6 => referral['field_1'],
        :MMERGE7 => referral['field_2'],
        :MMERGE8 => referral['field_3'],
        :MMERGE9 => referral['field_4'],
        :MMERGE11 => referral['field_5'],
        :MMERGE12 => referral['field_6'],
        :MMERGE13 => referral['field_7'],
        :MMERGE14 => referral['field_8'],
        :MMERGE15 => referral['field_9'],
        :FNAME => referral['first_name']
        } 
      }
    end
    @log.info("prepared_batch : #{prepared_batch}")
    result = @gibbon.lists.batch_subscribe(
      :id => @mc_list_id, 
      :batch => prepared_batch,
      :double_optin => false,
      :update_existing => true
    )
    @log.info("#{result}")
  rescue Exception => e
    @log.warn("Unable to load batch into mailchimp because #{e.message}")
  end
end