When I start the X11.app then it launches an xterm automatically. I've long since switched from the "ordinary" xterm to rxvt-unicode so the initial xterm just hangs around like a wallflower never being used. Whilst it's not particularly bad, it spoils the look of the place so I'd like to stop it launching. How do I do it?
in a Terminal. However, note that there really shouldn't be necessary to every start XQuartz.app (or X11.app; see the comments) manually. It will start automatically when you run an X11 client, and then it will not start its defaults startup application.
Since I'm not at my OSX computer right now, I'll give you the fail-proof answer for this. 'true' does nothing and exits successfully, so I set that to run at startup.
Apple's old X11:
and for XQuartz:
and for MacPorts X11.app:
In case you are wondering,
I have additionally read that you can set these to