Intel Backlight CLI

backlight.sh

#!/bin/sh
#
# Author: Panji Kusuma <epanji at gmail dot com>
#
# Assume user already in video group
# Place these 3 lines in /etc/rc.d/rc.local and uncomment the lines
#
# echo 100 > /sys/class/backlight/intel_backlight/brightness
# chmod 664 /sys/class/backlight/intel_backlight/brightness
# chown root:video /sys/class/backlight/intel_backlight/brightness

DEBUG=${DEBUG:-0}
RESULT=${RESULT:-100}

if [[ $1 =~ ^[0-9+-]+$ ]]; then
    cd /sys/class/backlight/intel_backlight
    read MAX < max_brightness
    read CUR < brightness
    MIN=$(($MAX / 20))
    if [[ $1 =~ ^[+-]$ ]]; then
        RESULT=$(($CUR $1 $MIN))
    else
        RESULT=$1
    fi
else
    echo "Usage:"
    echo "  $0 <arg>"
    echo ""
    echo "The <arg> could be +, - or any integer."
    echo ""
    exit 1
fi

# RESULT should be within MIN and MAX
if [[ $RESULT -gt $MAX ]]; then
    RESULT=$MAX
elif [[ $RESULT -le 0 ]]; then
    RESULT=$MIN
else
    RESULT=${RESULT#-}
fi

# Main
if [[ $DEBUG -eq 0 ]]; then
    echo $RESULT >> brightness 2> /dev/null
else
    echo $RESULT
fi

exit 0