brightness.sh

#!/bin/bash

FILE='/sys/class/backlight/intel_backlight/brightness'

VALUES=(500 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 12421)
DEFAULT=9

current=$(cat $FILE)
current=${current,,}
case "$1" in
    set|reset)
        if [ -n "$2" ]; then
            new=${2,,}
        else
            new=${VALUES[DEFAULT]}
        fi
        if [ $new -ge ${VALUES[0]} ] && [ $new -le ${VALUES[${#VALUES[@]} - 1]} ]; then
            if echo $new >$FILE; then
                echo "Brightness set from $current to $new"
            else
                exit 2
            fi
        else
            echo "Incorrect brightness value: $new" >&2
            exit 1
        fi
        ;;
    up|down)
        for i in $(seq 0 $((${#VALUES[*]}-1))); do
            if [ "${VALUES[$i]}" == "$current" ]; then
                break
            fi
        done
        if [ "${VALUES[$i]}" != "$current" ]; then
            i=$DEFAULT
        fi
        case "$1" in
        up)
            i=$((i+1))
            if [ "$i" -eq "${#VALUES[*]}" ]; then
                echo "Brightness is already maximal"
            else
                 new=${VALUES[$i]}
                 $0 set $new >/dev/null 2>&1 && echo "Brightness increased from $current to $new"
            fi
            ;;
        down)
            i=$((i-1))
            if [ "$i" -eq "-1" ]; then
                echo "Brightness is already minimal"
            else
                 new=${VALUES[$i]}
                 $0 set $new >/dev/null 2>&1 && echo "Brightness decreased from $current to $new"
            fi
            ;;
        esac
        ;;
    *)
        echo "Current brightness is $current"
        ;;
esac