🔋 💻 Brightness-Battery-AC-power-script with notifications

Script to automatically adjust screen brightness based on battery or AC power status on a Linux system with Hyprland and notifies you.
The script checks every 5 seconds on the power state.

📜 Script path: ~/.config/scripts/battery-brightness-watcher.sh

#!/bin/bash

#export DBUS_SESSION_BUS_ADDRESS="unix:path=/run/user/$(id -u)/bus"

Environment=DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/%U/bus

while ! busctl --user --list | grep -q org.freedesktop.Notifications; do
    sleep 1
done

LAST_STATE=""
LOW_BATTERY_TRIGGERED=0

notify() {
    notify-send -u normal -a "Battery status" "$1" "$2" -h int:transient:1
}

BATTERY_CAPACITY_PATH="/sys/class/power_supply/BAT0/capacity"
AC_STATE_PATH="/sys/class/power_supply/AC/online"

while true; do
    if [ -f "$AC_STATE_PATH" ]; then
        AC_STATE=$(cat "$AC_STATE_PATH")
    else
        AC_STATE=""
    fi

    if [ -f "$BATTERY_CAPACITY_PATH" ]; then
        BATTERY_PERCENT=$(cat "$BATTERY_CAPACITY_PATH")
    else
        BATTERY_PERCENT=""
    fi

    if [ "$AC_STATE" = "1" ]; then
        NEW_STATE="AC"
    else
        NEW_STATE="BATTERY"
    fi

    if [ "$NEW_STATE" != "$LAST_STATE" ]; then
        if [ "$NEW_STATE" = "BATTERY" ]; then
            brightnessctl set 75%
            notify "󱊣 On battery" "brightness at 75%"
        else
            brightnessctl set 100%
            notify "󱐥 On AC power" "brightness at 100%"
            LOW_BATTERY_TRIGGERED=0
        fi
        LAST_STATE="$NEW_STATE"
    fi

    if [ -n "$BATTERY_PERCENT" ] && [ "$NEW_STATE" = "BATTERY" ]; then
        if [ "$BATTERY_PERCENT" -lt 20 ] && [ "$LOW_BATTERY_TRIGGERED" -eq 0 ]; then
            brightnessctl set 30%
            notify "󱊡 Battery below 20%" "brightness lowered at 30%"
            LOW_BATTERY_TRIGGERED=1
        elif [ "$BATTERY_PERCENT" -gt 25 ] && [ "$LOW_BATTERY_TRIGGERED" -eq 1 ]; then
            brightnessctl set 75%
            notify "Battery recovered" "brightness back at 75%"
            LOW_BATTERY_TRIGGERED=0
        fi
    fi

    sleep 5
done

⚙️ Systemd user service: ~/.config/systemd/user/battery-brightness.service

[Unit]
Description=Battery Brightness Watcher
After=hyprland-session.target
Wants=hyprland-session.target

[Service]
Type=simple
ExecStart=/home/[username]/.config/scripts/battery-brightness-watcher.sh
Restart=always
RestartSec=5

# Make sure session bus will be found:
Environment=DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/%U/bus
# (Optional: XDG_RUNTIME_DIR mostly /run/user/%U)
#Environment=XDG_RUNTIME_DIR=/run/user/%U

# Call Wayland variables only when necessary; DISPLAY=:0 is not needed in Wayland.
#Environment=DISPLAY=:0
#Environment=WAYLAND_DISPLAY=wayland-0

# (Make sure the script itself is executed with the right permissions; 
#  User is already in group video for Brightness.)
KillMode=process

[Install]
WantedBy=default.target

Replace YOUR_USERNAME with your actual Linux username.

▶️ Enable the systemd user service

systemctl --user daemon-reexec
systemctl --user daemon-reload
systemctl --user enable --now battery-brightness.service
systemctl --user status battery-brightness.service

Make sure to add yourself to video and input groups with

sudo usermod -aG video,input $User