Re: Emacs script options

[Sebastian Miele]

> From: Greg Minshall <minshall@umich.edu>
> Date: Fri, 2023-11-17 19:13 -0800
>
> hi.  i would like to be able to write Emacs scripts ("#!...") that allow
> a user to enter almost any option to the script itself, *without* having
> to use double dashes ("--") to avoid colliding with Emacs option
> processing.
>
> looking at "--script" and "-x", this doesn't seem possible.
>
> as a test case, given a simple script foo.sh (*), using "-x", and
> invoking it with an option "--eval" gives this error:
>
> ----
> % ./foo.sh --eval
> emacs: Option '--eval' requires an argument
> ----
>
> (that bare "--eval" *should* be an error if it were meant for Emacs
> itself; however, it is meant for the Emacs script, which may have other
> ideas of the syntax/semantics of "--eval".)
>
> the below patch to src/emacs.c (**) treats a "-x" (and its "partner"
> "-scripteval") like a "--" on the command line, and *seems* to allow
> arbitrary options on the command line.  for example, with this patch
> installed:
>
> ----
> % ./foo.sh --eval
> command-line-args-left (--eval)
> ----

On Linux that can be achieved by defining a custom interpreter.  E.g.,
put the following into ‘/path/to/emacs-script’:

  #!/bin/sh
  script=$1
  shift
  exec emacs -Q --batch --load $script -- "$@"

Then, with the following in a ‘test-script’

  #!/path/to/emacs-script
  ;; -*- mode: emacs-lisp; lexical-binding: t -*-
  (message "%s" command-line-args-left)

‘test-script --eval’ prints "(-- --eval)".

On Linux, and when ‘emacs-script’ is in the PATH, the ‘/path/to/’ in the
shebang even can be omitted.

However, the workaround is not possible on at least some non-Linux
systems, because not all systems allow something interpreted as an
interpreter in a shebang, see
https://en.wikipedia.org/wiki/Shebang_(Unix)#Syntax.