Sean McLemon

To learn more about Debian and Linux in general I'm selecting utilities at random from my PATH using the command below, learning what they do and writing a blog post about it. Previously: Part 1, Part 2, Part 3

    $ (for folder in `echo $PATH | sed "s/:/\\n/g"`; do ls -1 $folder; done; ) | shuf -n 1 | xargs man

Today's utility is xssstate, which lets your check the status of X window system's screensaver. It's written by the suckless guys, who've created a number of very good tools, such as surf (a minimalist web browser) and dmenu (autocompleting program launcher), both of which I use regularly.

The utility itself is pretty simple, there are only four command line switches including -v, so this will be pretty short post. First we can check if the screensaver is currently enabled using -t switch:

    $ xssstate -s
    off

Obviously the screensaver is off, since I am actively using this computer - however if the screensaver was active it'd print "on" and if it was disabled altogether you'd see "disabled".

To check the time idle in milliseconds, use the -i switch:

    $ xssstate -i
    2
    $ sleep 5 && xssstate -i
    4947

And to get time in milliseconds until the screensaver activates, invoke it with -t:

    $ xssstate -t
    599998
    $ sleep 10 && xssstate -t
    590052

The way the utility does this is by using some functionality provided by a X11 library, wrapped in a handful of switch statements (they have their own neat little github-style source browser if you want to check out xssstate.c in its entirety):

    // ...
    info = XScreenSaverAllocInfo();
    XScreenSaverQueryInfo(dpy, DefaultRootWindow(dpy), info);

    if (showstate) {
    	switch(info->state) {
	case ScreenSaverOn:
		printf("on\n");
		break;
	case ScreenSaverOff:
		printf("off\n");
		break;
	case ScreenSaverDisabled:
		printf("disabled\n");
		break;
	}
    } else if (showtill) {
	switch(info->state) {
	case ScreenSaverOn:
		printf("0\n");
		break;
	case ScreenSaverOff:
		printf("%lu\n", info->til_or_since);
		break;
	case ScreenSaverDisabled:
		printf("-1\n");
		break;
	}
    } else if (showidle) {
	printf("%lu\n", info->idle);
    }
    // ...

When I do these articles I like to show some practical real-life usage of the utility - in this case I decided to add a little timer to my xmobar showing how long my computer had been idle. To this I added a Run Com entry to my xmobarrc:

    -- also stick %xssstate% into the template
    Run Com "xssstate" [ "-t" ] "xssstate" 10,

This ends up showing with something like the below - apologies for shaky-cam!