Add 'xbackcalc'

xbackcalc

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+
+import sys
+
+p = "/sys/class/backlight/intel_backlight/brightness"
+
+with open(p, 'r') as f:
+    current = int(f.read())
+
+print("current brightness: {}".format(current))
+
+new = int(eval(
+    ' '.join(sys.argv[1:]),
+    {},
+    {'current': current},
+))
+
+print("new brightness: {}".format(new))
+
+with open(p, 'w') as f:
+    f.write(str(new))