Ruby script to set the brightness on my Dell XPS (the normal way fails after Ubuntu 13.04).

lux

#!/usr/bin/env ruby

if ARGV.length != 1 then
  puts 'Provide a single argument between 0.1 (nearly black) and 1.0 (max brigthness).'
  exit(42)
end

b = ARGV[0].to_f
b = (if b < 0.1 then 0.1 elsif b > 1.0 then 1.0 else b end).to_s

puts 'Setting brightness to ' + b
exec 'xrandr --output eDP1 --brightness ' + b