How to Determine if LCD Monitor is Turned on From Linux Command Line

Question

How do you tell if a computer\'s monitor(s) are turned on/off from the command line in Linux? I\'ve traditionally thought of monitors as output-only devices, but I\'ve noticed t

Answer 1

xset -qis the way to go for a raspberry pi. A check to see if the reply contains 'Monitor is On' is a great way to use a gpio pin to turn off an LCD Backlight;

if(runOSCommand("xset -q").contains("Monitor is On")){
            System.out.println("Monitor is On");
            if screenLight.isHigh()) {
                screenLight.low();
            }
        }else{
            System.out.println("Monitor is Off");
            if (screenLight.isLow()) {
                screenLight.high();
            }
        }


     public static String runOSCommand(String command){
     String s = null;
     String string = "";
     Process p;
     try {
         p = Runtime.getRuntime().exec(command);
         BufferedReader br = new BufferedReader(
             new InputStreamReader(p.getInputStream()));
         while ((s = br.readLine()) != null){
 //            System.out.println("line: " + s);
             string += s;
         }
         p.waitFor();
//         System.out.println ("exit: " + p.exitValue());
         p.destroy();
     } catch (Exception e) {}
     return string;
 }