Ruby script utilizing the ruby-gmail gem that allows for searching and downloading Gmail messages by label. This implementation is looking for invoice emails and parsing the amount of money that was transferred.

gmail-invoice-parse.rb

require 'gmail'

label = 'transactional/payment'
Gmail.new(username, password) do |gmail|
  puts "Emails that match label '#{ label }'"
  lender_profit = 0
  gmail.mailbox(label).emails.each do |email|
    message = email.message
    next if message.subject =~ /^Re: /
    next if message.subject =~ /^Fwd: /

    timestamp = message.date.to_time.to_i
    recipient_email = if message.to.is_a?(Enumerable)
                        message.to.first
                      else
                        message.to
                      end

    match = message.body.to_s[/your profit:\n\-?\$([0-9\.]*)/] ||
            message.body.to_s[/for a total of\n\$([0-9\.]*)/]

    # before 2013-06-03, we didn't put the profit rate in emails
    next if match.nil?

    profit = match.split('$').last.to_f
    profit *= -1 if match.include?(?-)

    puts [ timestamp, recipient_email, profit ].join(',')

    lender_profit += profit
  end
  puts "Total lender profit: $#{ lender_profit.round(2) }"
end