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focus-or-launch

Small script to focus or launch a program under X server.

demo

Introduction

I was annoyed with most DE / WM inability to define a keyboard shortcut doing the following:

  • attempt focus on a window for program, on current desktop, if any
  • launch the program as a fallback

This correspond to a use-case for which we don't want more than 1 instance of a program window per virtual desktop.

I ended up with this small script that does the trick.

It can act as a nice complement to xbindkeys & wmutils (albeit less minimal) for multi-desktop setups.

For more context, read the accompanying blog post.

General Usage

$ focus-or-launch --app-class <window-class> --app-launch-command '<launch-command>'
argument description
--app-class The program's window X window class
--app-launch-command The command to run to launch the program

Finding out the window class of a program

To find out the X window class of a window, run xprop in a terminal and then click on the window.

Search for the value of WM_CLASS(STRING).

In should be in the form "program", "Program".

You should then use the value program.Program as the argument for focus-or-launch.

Examples

All those examples take the following command, launching an Emacs client frame.

Manual execution

$ focus-or-launch --app-class emacs.Emacs --app-launch-command 'emacsclient -c'

xbindkey

Put this entry in your ~/.xbindkeysrc:

"focus-or-launch --app-class emacs.Emacs --app-launch-command 'emacsclient -c'"
    Mod4 + e

Gnome3

Go to Settings > Keyboard Shortcuts, all the way down and click on the + to add a custom shortcut.

gnome_shortcut_settings

Dependencies

  • python 3
  • wmctrl
  • xdotool

Implementation details

wmctrl is used to determine the list of windows for current desktop.

xdotool is used to list the windows for a given class.

They share the same id system for windows (property WM_TRANSIENT_FOR(WINDOW) as returned by xprop).

I also explored using commands xwininfo -root -children, xlsclients -l but they seemed to be using another id (property WM_CLIENT_LEADER(WINDOW) in xprop).

With xprop -id <window_id>, window_id being either one of the 2 id system, we could join the results.

But this is cumbersome and not necessary for our use-case.

Performance

The weak link in the chain is xdotool.

It is notorious for being slow.

Tested on a modern 64 bit processor with Ubuntu 20.04, performance is very good (< 5ms).

Tested on a old 32bit laptop with BunsenLabs Lithium, there is a noticeable delay (> 100ms).

References

Similar projects

u/narrow_assignment made a very similar script. His version is more suited for the use-case where you'd want a program to have its window on only one desktop at a time. It will launch program if not running of focus on an existing window in another desktop, switching to it. It's in pure bourne shell and relies on xprop and wmctrl.

There is a a script on the fluxbox wiki (at the end of the page) that relies solely on xdotool but I assume it does not distinguish between desktops.

StackOverflow user desgua shared another implementation that likewise doesn't distinguish between desktops.

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🏃 Small python script to focus or launch program under X server

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