Script to set brightness in steps. Never to 0.

setbrightness

# Set screen brightness
# Usage: setbrightness more|less|<int>

DIR="/sys/class/backlight/intel_backlight"
MAX_VALUE=$( < $DIR/max_brightness )
MAX_STEP=${MAX_STEP:-8}
STEP_AMOUNT=$(( $MAX_VALUE / $MAX_STEP ))
CURRENT_VALUE=$( < $DIR/brightness )
CURRENT_STEP=$((  $CURRENT_VALUE / $STEP_AMOUNT ))

# Echo to stderr
function print_err() {
  >&2 echo "$@"
}

# Set brightness by step value
function setstep() {
  STEP=$1
  if [[ $STEP -lt 1 || $STEP -gt $MAX_STEP ]]; then
    print_err "Invalid step $STEP. Expected number between 1 and $MAX_STEP"
    exit 1
  fi

  # Set brightness and exit with echo's exit code
  echo $(( $STEP * $STEP_AMOUNT )) | sudo /usr/bin/tee $DIR/brightness
  exit $?
}

if [ -z "$1" ]; then
  echo "Current screen brightness is at step $CURRENT_STEP ($CURRENT_VALUE)"
  exit 0
fi

case $1 in
  more ) setstep $(( $CURRENT_STEP + 1 )) ;;
  less ) setstep $(( $CURRENT_STEP - 1 )) ;;
  *) [[ $1 =~ ^[0-9]{1,2}$ ]] && setstep $1 || print_err "Invalid argument"; exit 1 ;;
esac