Returns an array of dates between two given dates. You can select the "step" (year, month, day)

inverval_dates.lua

-- Returns an array of dates between `date1` and `date2`
-- The 'step' between dates it can be selected with 3 possible values:
-- (year, month, day)
--
-- ie: get_interval_dates(20130101, 20130601, "month")
-- -> (201301, 201302, 201303, 201304, 201305, 201306)
--
-- Diego Navarro (dnmellen)
function get_interval_dates(date1, date2, step)
  local result = {}
  local i = 1

  local date1_time = os.time({year=string.sub(date1, 1, 4), month=string.sub(date1, 5, 6), day=string.sub(date1, 7, 8)})
  local date2_time = os.time({year=string.sub(date2, 1, 4), month=string.sub(date2, 5, 6), day=string.sub(date2, 7, 8)})

  local step_int = nil
  local step_fmt = nil

  if step == "day" then
    step_int = 86400
    step_fmt = "%Y%m%d"
  elseif step == "month" then
    step_int = 2678400
    step_fmt = "%Y%m"
  elseif step == "year" then
    step_int = 31536000
    step_fmt = "%Y%m"
  else
    return result
  end

  local date_aux = date1_time
  while date_aux < date2_time + step_int do
    result[i] = os.date(step_fmt, date_aux)
    date_aux = date_aux + step_int
    i = i + 1
  end

  return result
end


for i, line in ipairs(get_interval_dates("20130101", "20130601", "month")) do
  print(line)
end