local base = "/sys/devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/intel_backlight/"

function readnum(file)
  local f = io.open(base .. file,'r')
  local n = f:read("*number")
  f:close()
  return n
end

local cur = readnum("brightness")
local min = 0
local max = readnum("max_brightness")

print( string.format("[%s,%s] %s", min, max, cur) )