Adds keyboard backlight command

- Specifically for Mac

backlight

@@ -0,0 +1,105 @@
+#!/bin/sh
+ 
+# backlight_get
+#       Print current keyboard brightness from UPower to stdout.
+backlight_get()
+{
+    dbus-send --type=method_call --print-reply=literal --system         \
+        --dest='org.freedesktop.UPower'                                 \
+        '/org/freedesktop/UPower/KbdBacklight'                          \
+        'org.freedesktop.UPower.KbdBacklight.GetBrightness'             \
+        | awk '{print $2}'
+}
+ 
+# backlight_get_max
+#       Print the maximum keyboard brightness from UPower to stdout.
+backlight_get_max()
+{
+    dbus-send --type=method_call --print-reply=literal --system       \
+        --dest='org.freedesktop.UPower'                               \
+        '/org/freedesktop/UPower/KbdBacklight'                        \
+        'org.freedesktop.UPower.KbdBacklight.GetMaxBrightness'        \
+        | awk '{print $2}'
+}
+ 
+# backlight_set NUMBER
+#       Set the current backlight brighness to NUMBER, through UPower
+backlight_set()
+{
+    value="$1"
+    if test -z "${value}" ; then
+        echo "Invalid backlight value ${value}"
+    fi
+ 
+    dbus-send --type=method_call --print-reply=literal --system       \
+        --dest='org.freedesktop.UPower'                               \
+        '/org/freedesktop/UPower/KbdBacklight'                        \
+        'org.freedesktop.UPower.KbdBacklight.SetBrightness'           \
+        "int32:${value}}"
+}
+ 
+# backlight_change [ UP | DOWN | NUMBER ]
+#       Change the current backlight value upwards or downwards, or
+#       set it to a specific numeric value.
+backlight_change()
+{
+    change="$1"
+    if test -z "${change}" ; then
+        echo "Invalid backlight change ${change}."                    \
+            "Should be 'up' or 'down'." >&2
+        return 1
+    fi
+ 
+    case ${change} in
+    [1234567890]|[[1234567890][[1234567890])
+        current=$( backlight_get )
+        max=$( backlight_get_max )
+        value=$( expr ${change} + 0 )
+        if test ${value} -lt 0 || test ${value} -gt ${max} ; then
+            echo "Invalid backlight value ${value}."                  \
+                "Should be a number between 0 .. ${max}" >&2
+            return 1
+        else
+            backlight_set "${value}"
+            # notify-send -t 800 "Keyboard brightness set to ${value}"
+        fi
+        ;;
+ 
+    [uU][pP])
+        current=$( backlight_get )
+        max=$( backlight_get_max )
+        if test "${current}" -lt "${max}" ; then
+            value=$(( ${current} + 5 ))
+            backlight_set "${value}"
+            # notify-send -t 800 "Keyboard brightness set to ${value}"
+        fi
+        ;;
+ 
+    [dD][oO][wW][nN])
+        current=$( backlight_get )
+        if test "${current}" -gt 0 ; then
+            value=$(( ${current}  - 5 ))
+            backlight_set "${value}"
+            # notify-send -t 800 "Keyboard brightness set to ${value}"
+        fi
+        ;;
+ 
+    *)
+        echo "Invalid backlight change ${change}." >&2
+        echo "Should be 'up' or 'down' or a number between"           \
+            "1 .. $( backlight_get_max )" >&2
+        return 1
+        ;;
+    esac
+}
+ 
+if test $# -eq 0 ; then
+    current_brightness=$( backlight_get )
+    # notify-send -t 800 "Keyboard brightness is ${current_brightness}"
+else
+    # Handle multiple backlight changes, e.g.:
+    #   backlight.sh up up down down up
+    for change in "$@" ; do
+        backlight_change "${change}"
+    done
+fi