list_customers_by_coupon.rb

#!/usr/bin/env ruby

require 'stripe'

Stripe.api_key = 'API_KEY'

customers_by_coupon = {}
customer_count = nil
batch_count = 100
batch_offset = 0

# we can only load customer objects in batches of 100, so do that in this loop
while !customer_count || batch_offset < customer_count
  puts "Loading customers #{batch_offset}..#{batch_offset + batch_count}"
  customer_hash = Stripe::Customer.all(:count => batch_count, :offset => batch_offset)
  customer_count = customer_hash['count']
  customer_batch = customer_hash['data']
  batch_offset += customer_batch.length
  # filter out customers who have a coupon applied to them
  customers_with_discounts = customer_batch.select{|c| c['discount']}
  # store these customers in customers_by_coupon, keyed on coupon code
  customers_with_discounts.each do |customer|
    coupon_id = customer['discount']['coupon']['id']
    (customers_by_coupon[coupon_id] ||= []) << customer
  end
end
puts "Done loading customers!"

if customers_by_coupon.length > 0
  # print out a CSV list of "coupon_id, customer_id" pairs
  puts "\nCOUPON_ID, CUSTOMER_ID"
  customers_by_coupon.each do |(coupon_id,customers)|
    customers.each do |c|
      puts "#{coupon_id}, #{c.id}"
    end
  end
else
  puts "\nNo customers have discounts."
end