gistfile1.sh

#!/bin/bash
#
# Brightness script for the ASUS G74SX
#
# Arguments:
#   up   - increase brightness by 1
#   down - decrease brightness by 1
#

BRIGHTNESS=`cat /sys/devices/platform/asus-nb-wmi/leds/asus\:\:kbd_backlight/brightness`
MAX_BRIGHT=`cat /sys/devices/platform/asus-nb-wmi/leds/asus\:\:kbd_backlight/max_brightness`

# Try to recover brightness setting (since the `cat` seems to always return 0)
if [ -f /tmp/keyboard-brightness-ctl ]
then
  BRIGHTNESS=`cat /tmp/keyboard-brightness-ctl`
fi

case "$1" in
  up)
    BRIGHTNESS=$((BRIGHTNESS + 1))
    if [ $BRIGHTNESS -gt $MAX_BRIGHT ] ; then BRIGHTNESS=$MAX_BRIGHT ; fi
    echo $BRIGHTNESS > /tmp/keyboard-brightness-ctl
    echo $BRIGHTNESS > /sys/devices/platform/asus-nb-wmi/leds/asus\:\:kbd_backlight/brightness
  ;;

  down)
    BRIGHTNESS=$((BRIGHTNESS - 1))
    if [ $BRIGHTNESS -lt 0 ] ; then BRIGHTNESS=0 ; fi
    echo $BRIGHTNESS > /tmp/keyboard-brightness-ctl
    echo $BRIGHTNESS > /sys/devices/platform/asus-nb-wmi/leds/asus\:\:kbd_backlight/brightness
  ;;
esac

This is also valid for ASUS G75VW.