sync laptop and external monitor brightness

brightness.sh

#!/bin/bash

# This script syncs the brightness on my laptop screen as well as my
# Dell 2720QM external usb-c monitor

# References:
# https://blog.tcharles.fr/ddc-ci-screen-control-on-linux

# Steps
# 1. Add udev rules to /etc/udev/rules.d/45-ddcutil-i2c.rules:
# KERNEL=="i2c-[0-9]*", GROUP="victor", MODE="0660"
# 2. Get I2C bus ID:
# ddcutil detect
#
# Usage
# I have my keyboard brightness keys mapped in ~/.config/i3/config like this:
# bindsym XF86MonBrightnessDown exec "/home/victor/.config/i3/brightness.sh down"
# bindsym XF86MonBrightnessUp exec "/home/victor/.config/i3/brightness.sh up"
#
# I also set crontab to call the brightness and audio volumes based on time of day.

BUS_ID=5
INCREMENT=25

function getDellBrightness() {
    local busId=${BUS_ID}

    echo $(ddcutil --bus=$busId getvcp 10 | sed -n 's/.*current value =[[:space:]]*\(.*\),.*$/\1/p')
}

function setBrightness() {
    local level=$1
    local busId=${BUS_ID}

    # Set Dell brightness
    ddcutil --bus=$busId setvcp 10 $level

    # set laptop screen
    brightnessctl set $level%
}

function decrementBrightness() {
    current=$(getDellBrightness)
    new=$(python -c "print(max(1, $current - $INCREMENT))")

    setBrightness $new
}

function incrementBrightness() {
    current=$(getDellBrightness)
    new=$(python -c "print(min(100, $current + $INCREMENT))")

    setBrightness $new
}

function main() {
    action=$1

    is_number='^[0-9]+$'

    if [ "${action}" == "up" ]; then
        incrementBrightness
    elif [ "${action}" == "down" ]; then
        decrementBrightness
    elif [[ "${action}" =~ $is_number ]]; then
        setBrightness "${action}"
    fi
}

main $@