Re: emacsclient in elisp

[Jean Louis]

* Eli Zaretskii <eliz@gnu.org> [2021-05-20 22:46]:
> > Cc: monnier@iro.umontreal.ca, bugs@gnu.support, emacs-devel@gnu.org
> > From: Daniel Mendler <mail@daniel-mendler.de>
> > Date: Thu, 20 May 2021 21:10:37 +0200
> > 
> > Of course, there is another Emacs on the other side of the pipe. It is
> > Emacs all the way down ;)
> 
> But then I don't understand the importance of stdin in this context.
> If you want to read output from another program, just run that
> program, in this case another Emacs, as a subprocess.  Then anything
> that other program writes to its stdout will be read as part of normal
> machinery of reading sub-process output, including filters, sentinels,
> and all that.

Side note to your comment, I find it somehow good. So I could just
fake the STDIN reading by using for example `cat`. But it does not
work. Please if you have some reference to demonstration of the above,
let me know.

My expectation is for following to work:

process-org.el:

(defun cat ()
  (princ (shell-command-to-string "cat"))) ;; later call-process to be used

then on command line:

$ emacs -Q -l process-org.el --batch -f cat 

So that does not work, it exits immediately, it is not waiting for
stdin

And within Emacs (shell-command-to-string "cat") will also not wait,
including with call process, it will not wait.

But would it wait for STDIN just as `cat` does wait, then it would be
easy to use such external wrapper to receive STDIN and process it with
Emacs.

Thank you,
Jean Louis