Re: How to get DISPLAY of emacsclient?

[Gregory Heytings]

> I was seeking a way to avoid creation a visible frame and to call a 
> function that does not work without X connection.
>
> So I should thank Jim again for drawing my attention why the effect of 
> the --display option is stronger than for the DISPLAY environment. This 
> option indirectly solves the problem.

I still think this is an ill-posed problem, so here are a few additional 
thoughs, in case you find them useful.  There are at least three cases:

1. "emacsclient --eval '(+ 1 1)'" does NOT use a display: it is evaluated 
in the server process.  You can use '(getenv DISPLAY)' there, but it will 
not return any useful information, it will return the value of DISPLAY 
that was current when the Emacs daemon was created.

2. "emacsclient -c", which creates a frame on the display specified in the 
environment variable DISPLAY (if DISPLAY is unset, "emacsclient -c" is 
equivalent to "emacsclient -nw").

3. "emacsclient --display <DISPLAY> -c", which creates a frame on the 
specified display <DISPLAY>; it is equivalent to "env DISPLAY=<DISPLAY> 
emacsclient -c".

If you want to know the value if the environment variable DISPLAY in case 
1, the best way to do that is to explicitly include "$DISPLAY" in the form 
you evaluate, e.g. like this:

emacsclient --eval '(progn (setq display "'$DISPLAY'") (princ display))'