How to know which window has focus and how to change it?

Question

I would like to know how can I ask X11 which windows has focus. And if for any reason my own application (that may be visible or not) got the focus I want be able to let the

Answer 1

I recommend an application called XDoTool. It supports quite a lot of queries, controls, and even hooks.

> xdotool getwindowfocus               # 29360135
> xdotool getwindowfocus getwindowpid  # 12988
> xdotool getwindowfocus getwindowname # tilda
> xdotool getwindowfocus behave '%@' blur getmouselocation
#      or focus, mouse-enter, etc.
x:514 y:317 screen:0 window:56623121
x:271 y:26 screen:0 window:56623121
...

Commands like behave accept a callback, which can be built-in like getmouselocation or external like exec notify-send 'focused window', exec zsh myscript.zsh, etc., however you want to use it.

Edit - you can focus using xdotool windowfocus [options] [window], as in xdotool search --class firefox windowfocus. In my case this causes errors because Firefox shows up as a couple dozen 'windows', but all have the same PID; it works given the right ID. Hopefully that's a start.

Edit 2 - the 'window ID' is the decimal representation of the window pointer, e.g. from xprop:

> xprop -root _NET_ACTIVE_WINDOW
_NET_ACTIVE_WINDOW(WINDOW): window id # 0x1c00007, 0x0
> xdotool getwindowfocus
29360135
> printf '%d\n' '0x1c00007'
29360135