Wonky-ass script to adjust brightness on my Asus laptop running Crunchbang and Arch Linux.

bright.py

#!/usr/bin/env python
"""
Adjust screen brightness.
Usage: `bright 10`
Default is to adjust brightness via hardware.
'-s' flag will make the tool adjust brightness via software.
'-g' flag prints current brightness (hardware)
Use '-d' and '-i' to decrement and increment, respectively. (hardware)
TODO: make '-sg' show software brightness
"""
from __future__ import division
from argparse import ArgumentParser
from subprocess import call, check_call
from sys import exit

BRIGHTNESS_FILE = '/sys/class/backlight/acpi_video0/brightness'
MAX_BRIGHTNESS =  '/sys/class/backlight/acpi_video0/max_brightness'

def get_max(args):
  "Get max brightness as int"
  if args.soft:
    return 10 # software is in range 0.0 -> 1.0, or 0 -> 10
  else:
    try:
      with open(MAX_BRIGHTNESS, 'r') as f:
        return int(f.read())
    except Exception:
      return 15 # this is the max when i wrote this...

def get_curr():
  "Get current brightness (hardware only). False on failure"
  try:
    with open(BRIGHTNESS_FILE, 'r') as f:
      return int(f.read())
  except Exception:
    return False

def fail():
  print('FAIL')
  exit(1)

def donezo():
  print("Nothing to do.")
  exit(0)

parse = ArgumentParser(description='Adjust blacklight brightness')
parse.add_argument('-s', '--soft', action='store_true',\
  help='Adjust brightness from software. Default is hardware.')
parse.add_argument('-g', '--get', action='store_true',\
  help='Display brightness instead of setting it')
parse.add_argument('-i', '--inc', action='store_true',\
  help='Increment brightness 1 notch. Hardware only.')
parse.add_argument('-d', '--dec', action='store_true',\
  help='Decrement brightness 1 notch. Hardware only.')
parse.add_argument('num', nargs='?', type=int, help='Brightness value')

args = parse.parse_args()

if args.get:
  curr = get_curr()
  if curr is not False:
    print("%d of %d" % (curr, get_max(args)))
    exit(0)
  fail()

# set max and min values
mn = 0
mx = get_max(args)

if args.dec:
  curr = get_curr()
  if curr <= 0:
    donezo()
  nxt = curr-1
elif args.inc:
  curr = get_curr()
  if curr >= mx:
    donezo()
  nxt = curr+1
elif args.num is None:
  parse.print_help()
  exit(1)
else:
  nxt = args.num

if nxt < mn or nxt > mx:
  print("Brightness must be between %d and %d" % (mn, mx))
  exit(1)

# increment and decrement not supported for software
if args.soft and not args.dec and not args.inc:
  check_call(['xrandr','--output','LVDS1','--brightness',str(nxt/10)])
else:
  check_call([
    'sudo','-u','root','bash','-c','echo -n %d > %s' % (nxt,BRIGHTNESS_FILE)
  ])

exit(0)