sb-battery: notification on very low battery level

.local/bin/statusbar/sb-battery

@@ -28,28 +28,44 @@ do
 			continue
 		fi
 
+		# Critical low-battery notification at the "!" level (<=5% and discharging).
+		# Notify only once per discharge episode: a flag in /tmp suppresses repeats
+		# and is cleared the moment we stop discharging (plug in) or on reboot
+		# (since /tmp is wiped), so the next low event notifies again.
+		lowflag="/tmp/battery_low_notified_${battery##*/}"
+		if grep -q "Discharging" "$battery"/status; then
+			if [ "$capacity" -le 5 ] && [ ! -f "$lowflag" ]; then
+				notify-send -u critical "❗ Battery critically low" \
+					"Battery at ${capacity}%. Plug in the laptop now."
+				touch "$lowflag"
+			fi
+		else
+			# Plugged in (charging / not charging / full): arm for the next episode.
+			rm -f "$lowflag"
+		fi
+
 		unset status
 		status=$(sed "s/Not charging/🛑/" "$battery"/status)
 		# Center picture around the actual capacity.
 		# Displayable capacities: 0, 1/4, 1/2, 3/4, 1 -> intervall of length 25% centered around displaycategory
 		# -> +- 12.5% for every level
 		if grep -qE "(Discharging|Charging)" "$battery"/status; then
-			status=
+			status=" "
 			[ "$capacity" -le 87 ] &&
-				status=""
+				status=" "
 			[ "$capacity" -le 63 ] &&
-				status=""
+				status=" "
 			[ "$capacity" -le 37 ] &&
-				status=""
+				status=" "
 			[ "$capacity" -le 13 ] &&
-				status=""
+				status=" "
 			[ "$capacity" -le 5 ] &&
-				status="❗"
+				status=" ❗"
 			if grep -q "Charging" "$battery"/status; then
 				status="${status}🔌"
 			fi
 		fi
-		printf "%s \n" "$status"
+		printf "%s\n" "$status"
 	else
 		echo "Error. Capacity:$capacity" > /dev/stderr #if battery fails during reading, quit
 	fi