#!/bin/bash
pas="0.05"
mini="0.2"
ECRAN=`xrandr | grep -i "^.* connected" | cut -f1 -d" "`
if [ -f /tmp/gamma.tmp ]; then
   g="$(cat /tmp/gamma.tmp)"
   [ 1 -eq `echo "$g > $mini" | bc` ] && g="$(echo $g-$pas | bc)"
else
   g="$(echo 1-$pas | bc)"
fi
echo $g>/tmp/gamma.tmp
xrandr --output $ECRAN --gamma $g:$g:$g