On Tue, Oct 29, 2019 at 02:32:39PM +0900, John Crawley wrote: > A (bash) script wants to put up a GUI (yad) if it can, or otherwise > try to interact with the user on the terminal. > > Previously I was using loginctl: > loginctl show-session -p Type $XDG_SESSION_ID > and looking for 'Type=x11' or 'Type=wayland' > > However, if a user logs in on a tty and then runs 'startx' (I don't > know if Wayland has an equivalent) then the above command returns > 'Type=tty' even when X is running. > ($XDG_SESSION_TYPE gives the same results.) > > I've replaced the test with > [[ -n $DISPLAY || -n $WAYLAND_DISPLAY ]] && <use GUI> > but environment variables are a bit fragile and I was wondering if > there might be a better way.
What is fragile about the environment?
First you'll have to find out what you are after. Note that there
may be several X sessions around in your box, that the X server
may be a remote one, that your application may be displaying things
on several X displays at once (I know, Gtk is, or used to be,
particularly buggy about that -- but we ain't going to go Microsoft's
way [1] about this, are we?
So yes, in the general case, there may be (way) more than one
graphical session to choose from: if you're looking for a criterion
to pick "the obvious one", then you'll have to specify your
criterion yourself.
Thus, environment is just about the right tool: a process inherits
its ancestor's environment -- and somewhere up the chain there is
the process "representing" the session (embodied in X by all that
Xsession stuff, where the variables are set).
The "startx" thing you mention is particularly misleading: the
shell where you'd issue "startx" from is *not" "in" the session!
Cheers
[1] declaring darkness as industry standard
https://www.barrypopik.com/index.php/new_york_city/entry/how_many_microsoft_engineers_does_it_take
-- tomás
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