Hook for a specific window losing focus?

[097115]

If I want to run a script when I switch to a specific window, then I can do something like this:

tmux set-hook session-window-changed[101] 'if-shell -F "#{m/r:^my-window$,#W}" "run-shell my-script"

But what if I want to run a script when switching from this very window? At first, I thought maybe something like this could work:

tmux set-hook session-window-changed[101] 'if-shell -F "#{m/r:^my-window$,#{hook_window_name}}" "run-shell my-script"

But it seems like it doesn't.

Then I remembered the pane-focus-out hook. But with more panes in that window it gets too complex, and it's also triggered by display-menu.

So, maybe there's a more correct way? That would only trigger exactly on switching away from this window?

Thanks :)

[nicm]

Yes... because this is a session hook, there is no hook_window_name. Try this:

--- session.c   30 Mar 2025 22:01:55 -0000      1.100
+++ session.c   22 Jul 2025 07:50:13 -0000
@@ -502,7 +502,10 @@ session_set_current(struct session *s, s
        winlink_clear_flags(wl);
        window_update_activity(wl->window);
        tty_update_window_offset(wl->window);
-       notify_session("session-window-changed", s);
+       if (old != NULL)
+               notify_session_window("session-window-changed", s, old->window);
+       else
+               notify_session("session-window-changed", s);
        return (0);
 }

[097115]

I tried these two hooks (with the master with your patch applied, all previous sessions closed, a new one started with the newly built ./tmux):

./tmux set-hook session-window-changed[101] 'if-shell -F "#{m/r:^my-window$,#{window_name}}" "display-message \"TO?\""'
./tmux set-hook session-window-changed[102] 'if-shell -F "#{m/r:^my-window$,#{hook_window_name}}" "display-message \"FROM?\""'

And they both seem to fire when switching from. The first one, [101], previously used to trigger when switching to.

I did miss something?

[nicm]

Yeah precisely the default target would have been the session's current window which would be the one you are switching to.

What if you do if -t:?

[097115]

What if you do if -t:?

Still both trigger when switching from.

[nicm]

Yeah it is tricky because now it assumes you want the previous window, not the current one, so we need a way to get the current window or a way to get the previous window without the diff.

If you try without the diff, does -t:{last} work to get you the previous window?

[097115]

Ah! That seems to work! (I had to enquote {last}, said syntax error otherwise :)

---

So, for the record, this one works when switching FROM a window named TEST (executes date in a window that becomes active after switching from the aforesaid window):

tmux set-hook session-window-changed[101] 'if-shell -t:"{last}" -F "#{m/r:^TEST$,#{window_name}}" "send-keys date Enter"'

And this one, as we already knew, works when switching TO a window named TEST (executes date in a window named TEST after switching to it):

tmux set-hook session-window-changed[102] 'if-shell -F "#{m/r:^TEST$,#{window_name}}" "send-keys -t TEST date Enter"'

Thanks a lot, Nicholas!

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