Command line utility to switch between full and low brightness using xbacklight.

sween.bash

#!/usr/bin/env bash

if [[ $* == *-h* ]]; then
  cat <<USAGE
Switch between full and low brightness using xbacklight.

  sween [low-brightness]
    low-brightness defaults to 5, and is a percentage.
USAGE
  exit 1
fi

LOW_BRIGHTNESS=${1:-5}
FULL_BRIGHTNESS=100
MID_BRIGHTNESS=$(( (100 - $LOW_BRIGHTNESS) / 2 + $LOW_BRIGHTNESS ))
CURRENT_BRIGHTNESS="$(xbacklight)"
CURRENT_BRIGHTNESS=${CURRENT_BRIGHTNESS%.*}

if (( $CURRENT_BRIGHTNESS > $MID_BRIGHTNESS )); then
  BRIGHTNESS=$LOW_BRIGHTNESS
else
  BRIGHTNESS=$FULL_BRIGHTNESS
fi

STEPS=$(( $CURRENT_BRIGHTNESS - $BRIGHTNESS ))
if (( $STEPS < 0 )); then
  STEPS=$(( $STEPS * -1 ))
fi

TIME=$(( $STEPS * 10 ))

xbacklight = $BRIGHTNESS -time $TIME -steps $STEPS &