check whether emacs session is running under local X server

check whether emacs session is running under local X server

[Roland Winkler]

In my .emacs I would like to distinguish between an emacs session
running under the local X server and an emacs session running under
a remote X server. I expect that the $DISPLAY variable can do the
job. But I am not familiar with the details.
(Once upon a time I set $DISPLAY manually. Nowadays I use ssh which
handles $DISPLAY for me, but I do not understand the scheme it uses.)

What can I do?
Thanks,

Roland

Re: check whether emacs session is running under local X server

[Eric Hanchrow]

>>>>> "Roland" == Roland Winkler <Roland.Winkler@physik.uni-erlangen.de> writes:

    Roland> In my .emacs I would like to distinguish between an emacs
    Roland> session running under the local X server and an emacs
    Roland> session running under a remote X server.  I expect that
    Roland> the $DISPLAY variable can do the job.  But I am not
    Roland> familiar with the details.  (Once upon a time I set
    Roland> $DISPLAY manually.  Nowadays I use ssh which handles
    Roland> $DISPLAY for me, but I do not understand the scheme it
    Roland> uses.)

I don't think there's a 100% foolproof way, but here's how I do it:

(Isn't this awful?)

(let ((x-running-locally
       (and
        (boundp 'window-system)
        (or (eq (assoc-default 'window-system (frame-parameters current-frame)) 'x)
            (and (assq 'font (frame-parameters current-frame))
                 (assq 'display (frame-parameters current-frame))))
        (getenv "DISPLAY")

        (let ((display-data (split-string (getenv "DISPLAY") ":")))
          (if (= 1 (length display-data)) ; e.g. ("0")

              ;; e.g. ("offby1" "0")
              (setq display-data (cons (car (split-string (system-name) "\\.")) display-data))

            (let* ((display-host (nth 0 display-data))
                   (display-number (car (read-from-string (nth 1 display-data)))))
              ;; display numbers >=10 imply we're using SSH from a remote
              ;; machine
              (and (< display-number 10)
                   ;; (string-equal (downcase (car (split-string display-host "\\.")))
                   ;;                           (downcase (car (split-string (system-name)"\\."))))
                   ))))))
      ))

-- 
When it comes to electronic voting, most liberals are just plain
old-fashioned nuts.
        -- Joe Andrew, former chairman of the Democratic National
           Committee

Re: check whether emacs session is running under local X server

[Roland Winkler]

Eric Hanchrow <offby1@blarg.net> writes:

> (Isn't this awful?)

I had expected something like this...

>         (or (eq (assoc-default 'window-system (frame-parameters current-frame)) 'x)

What is the value of current-frame? The return value of (selected-frame)?

Thanks,

Roland

Re: check whether emacs session is running under local X server

[Eric Hanchrow]

>>>>> "Roland" == Roland Winkler <Roland.Winkler@physik.uni-erlangen.de> writes:

    >> (or (eq (assoc-default 'window-system (frame-parameters
    >> current-frame)) 'x)

    Roland> What is the value of current-frame?  The return value of
    Roland> (selected-frame)?

Oops!  Yes.

-- 
The woods aren't any drier than they were in 2000, but there
are a lot more people with matches.
        -- Doug Chapin, Electionline.org

Re: check whether emacs session is running under local X server

[Glenn Morris]

Roland Winkler wrote:

> In my .emacs I would like to distinguish between an emacs session
> running under the local X server and an emacs session running under
> a remote X server. I expect that the $DISPLAY variable can do the
> job. But I am not familiar with the details.
> (Once upon a time I set $DISPLAY manually. Nowadays I use ssh which
> handles $DISPLAY for me, but I do not understand the scheme it uses.)

I just check whether the SSH_CLIENT environment variable is set or
not.

Re: check whether emacs session is running under local X server

[Roland Winkler]

Glenn Morris <rgm+news@stanford.edu> writes:
>> In my .emacs I would like to distinguish between an emacs session
>> running under the local X server and an emacs session running under
>> a remote X server. I expect that the $DISPLAY variable can do the
>> job. But I am not familiar with the details.
>> (Once upon a time I set $DISPLAY manually. Nowadays I use ssh which
>> handles $DISPLAY for me, but I do not understand the scheme it uses.)
>
> I just check whether the SSH_CLIENT environment variable is set or
> not.

Thanks a lot! It seems that this is exactly what I was looking for.

Roland

Re: check whether emacs session is running under local X server

[Eric Hanchrow]

>>>>> "GM" == Glenn Morris <rgm+news@stanford.edu> writes:

    GM> I just check whether the SSH_CLIENT environment variable is
    GM> set or not.

Wish I'd thought of that :-)
-- 
The woods aren't any drier than they were in 2000, but there
are a lot more people with matches.
        -- Doug Chapin, Electionline.org