Improve backlight

i3/backlight.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -euo pipefail
+
 # Control screen brightness in a logarithmic fashion. Linear backlight control
 # just annoys me: I want fine-grained control over low brightnesses and quickly
 # change the value at high brightnesses.
@@ -22,20 +24,40 @@ pgrep -u $UID -x xbacklight >/dev/null && exit
 
 # Calculate new target brightness
 current_brightness=$(xbacklight -get)
-case $1 in
-	up)
-		target=$((current_brightness * $change_percent / 100))
-		[ $target -ne $current_brightness ] || target=$((target + 1))
-		;;
-	down)
-		target=$((current_brightness * 100 / $change_percent))
-		[ $target -ne $current_brightness ] || target=$((target - 1))
-		;;
-esac
 
-# Boundaries: can't go higher than 100% or lower than 1%
+new_target() {
-[ $target -le 1   ] && target=1
+	echo $current_brightness >&2
-[ $target -ge 100 ] && target=100
+	case $1 in
+		up)
+			if [ $current_brightness = 0 ]; then
+				echo 1
+				return
+			fi
 
+			target=$((current_brightness * $change_percent / 100))
+			[ $target -ne $current_brightness ] || target=$((target + 1))
+			;;
+
+		down)
+			if [ $current_brightness = 0 ]; then
+				echo 0.1
+				return
+			fi
+
+			target=$((current_brightness * 100 / $change_percent))
+			[ $target -ne $current_brightness ] || target=$((target - 1))
+			;;
+	esac
+
+	# Boundaries
+	if [ $target -le 1   ]; then echo 0.1; return; fi
+	if [ $target -ge 100 ]; then echo 100; return; fi
+
+	echo $target
+}
+
+target=$(new_target "$1")
+
+echo $target
 # Smoothly set the new brightness
 xbacklight -time 100 -fps 60 -set $target