logfile.txt

I, [2015-11-11T12:43:21.813873 #53754]  INFO -- random number: 7358696
I, [2015-11-11T12:43:21.814242 #53754]  INFO -- random number: 4563567

random.rb

require 'logger'

class Charlie
  def random_number
    rand(10000000)
  end
end

c = Charlie.new
p rand1 = c.random_number
p rand2 = c.random_number

logger = Logger.new('./logfile.txt') 
logger.info('random number #1') { rand1 }
logger.info('random number #2') { rand2 }
logger.close