brightness setting for i3 (using Gnome utility)

#!/usr/bin/env bash

# set -x

# /usr/lib/gnome-settings-daemon/gsd-backlight-helper
#Application Options:
#  --set-brightness         Set the current brightness
#  --get-brightness         Get the current brightness
#  --get-max-brightness     Get the number of brightness levels supported

GNOME_BL_HELPER="/usr/lib/gnome-settings-daemon/gsd-backlight-helper"
DELTA=54

brightness () {
    MAX_VAL=$( $GNOME_BL_HELPER --get-max-brightness )
    MIN_VAL=0
    CURR_VAL=$( $GNOME_BL_HELPER --get-brightness )
    SIGN=$1

    case "$SIGN" in
        "+")
            DIFF=$( echo "$MAX_VAL-$CURR_VAL" | bc -l )
            if [ "$DIFF" -gt $DELTA ]; then
                NEW_VAL=$( echo "$CURR_VAL $SIGN $DELTA" | bc -l )
            else
                NEW_VAL=$( echo "$CURR_VAL $SIGN $DIFF" | bc -l )
            fi
            echo "Setting new brightness: $NEW_VAL"
            pkexec $GNOME_BL_HELPER --set-brightness $NEW_VAL
            ;;
        "-")
            DIFF=$( echo "$CURR_VAL $SIGN $DELTA" | bc -l )
            if [ "$DIFF" -gt $DELTA ]; then
                NEW_VAL=$( echo "$CURR_VAL $SIGN $DELTA" | bc -l )
            else
                NEW_VAL=$MIN_VAL
            fi
            echo "Setting new brightness: $NEW_VAL"
            pkexec $GNOME_BL_HELPER --set-brightness $NEW_VAL
            ;;
        *)
            echo "Current brightness: $CURR_VAL"
    esac
}

case "$1" in
    inc)
        brightness "+"
        ;;
    dec)
        brightness "-"
        ;;
    *)
        brightness show
esac

exit 0