date-listgen.rb

#!/usr/bin/env ruby
# Generates list of dates according to a format passed as an argument
# Example: date-listgen.rb '%Y-%m-%d'
# 2015-02-01

require 'date'

def list_dates(format)
  if format.nil?
    format = '%d%m%Y'
  end
  d = Date.new(1900,1,1)
  today = Date.today
  begin
    d = d + 1
    puts d.strftime(format)
  end until d == today
end

list_dates(ARGV[0])