When `emacs` is started, use `emacsclient` instead if there is a server

Question

Most modern editors don't have a separate <editor>client binary. Instead, the main binary acts as a client to open a new window/the file given as an argument when possible.

Is there a way to accomplish the same in Emacs? I know about emacsclient but 1. it's not a drop-in replacement and 2. using it comfortably requires additional setup beyond copying .emacs.d to a machine -- e.g. adding a desktop file for emacsclient.

I'm envisioning something like this:

;; Start of init.el
(if (server-running-p)
    ;; Open given file in existing server
  (server-start))

Answer 1

Nowadays several megabytes are no problem for a client program. So maybe the problem of the size of Emacs is no longer that relevant.

With Emacs 27 you can run stuff in ~/.emacs.d/early-init.el before the initial frame opens. There you can try:

(require 'server)
(if (server-running-p "server")
  (let ((file-name (expand-file-name (car (cdr command-line-args)))))
    (unwind-protect
        (server-eval-at "server" `(find-file ,file-name))
      (kill-emacs)))
  (message "Server not running."))
(server-start)

If you run emacs somefile when the Emacs server is already running somefile should be opened in the server.

This is just a proof of principle. The handling of the argument is very rudimentary. One has to refine the argument handling if one wants to use that principle for production.

I only have emacs26 on my machine. Therefore, I cannot test the early-init.el-approach. If I put the above code into ~/.emacs it opens the file given on the command line in the already running server but the client opens an initial frame before it runs the code. So there is some kind of flicker.

Answer 2

The alternative-editor option supports this. The following invocation does what you describe:

emacsclient -a""

This opens emacsclient, and starts the server if it isn't already running.

See the manual for details: https://www.gnu.org/software/emacs/manual/html_node/emacs/Invoking-emacsclient.html

Answer 3

Would something like this work for you? You can save it as a script in PATH and run it instead of emacs or emacsclient.

#!/bin/bash

export REAL_EMACS_START=1
emacsclient $@ || emacs $@

EDIT:

If you want user to run emacs directly and achieve similar result, you can add the following to the top of init.el:

(unless (getenv "REAL_EMACS_START")
  (call-process-shell-command
   (format "export REAL_EMACS_START=1; (%sclient || %s) &" invocation-name invocation-name))
  (kill-emacs))