#!/bin/bash

export DISPLAY=:0

# no message if one is displayed already
if [[ "$(ps -efww | grep gxmessage | grep -v grep)" != "" ]]; then
    exit
fi
# no message if xscreensaver active
if [ "$(ps -efww | grep xscreensaver | grep -v grep)" != "" ]; then
    exit
fi
# no message if gnome-screensaver active
if [ "$(gnome-screensaver-command --query | grep is.active)" != "" ]; then
    exit
fi

gxmessage 'Rest your eyes!'