scripts: update backlight script

now goes up and down, no cycling

requires xbacklight and whatnot, acpibacklight works

.config/i3/config

@@ -81,7 +81,8 @@ bindsym $mod+Right  focus right
 # split in horizontal orientation
 bindsym $mod+b split h
 
-bindsym $mod+shift+b exec scripts/backlight-cycle.sh
+bindsym $mod+shift+b exec scripts/backlight-cycle.sh up
+bindsym $mod+shift+v exec scripts/backlight-cycle.sh down
 
 # split in vertical orientation
 bindsym $mod+v split v

scripts/backlight-cycle.sh

@@ -5,8 +5,25 @@ set -x
 
 current=$(xbacklight -get)
 
-next=$(( $current + 10))
+# can take args 'up' or 'down'
+case $1 in
+  up)
+    next=$(( $current + 10))
+    ;;
+  down)
+    next=$(( $current - 10))
+    ;;
+  *)
+    echo "Usage: backlight-cycle.sh [up|down]"
+    exit 1
+    ;;
+esac
+
+# clamping
 if (( next > 100 )); then
+  next=100
+fi
+if (( next < 0 )); then
   next=0
 fi