Run elisp program without Emacs?

Question

elisp is a good language, I find it can handle all kind of jobs, but can I use it like a shell script?

i.e. execute some *.el files from the console, without launching Emacs. Or launch Emacs, but don't enter interactive mode.

Answer 1

You can most definitely run elisp scripts in Emacs without starting the editor interface.

Here are the notes I've made/copied from a few extremely useful Q&As on the subject here at S.O. (and the following two in particular).

• Emacs shell scripts - how to put initial options into the script?
• Idiomatic batch processing of text in Emacs?

Much of this information, and more besides, is also covered in the following excellent overview, which is recommended reading:

• https://swsnr.de/blog/2014/08/12/emacs-script-pitfalls/

;;;; Elisp executable scripts

;; --batch vs --script
;; M-: (info "(emacs) Initial Options") RET
;; M-: (info "(elisp) Batch Mode") RET

;; Processing command-line arguments (boiler-plate)
;; http://stackoverflow.com/questions/6238331/#6259330 (and others)
;;
;; For robustness, it's important to both pass '--' as an argument
;; (to prevent Emacs from trying to process option arguments intended
;; for the script), and also to exit explicitly with `kill-emacs' at
;; the end of the script (to prevent Emacs from carrying on with other
;; processing, and/or visiting non-option arguments as files).
;;
;; #!/bin/sh
;; ":"; exec emacs -Q --script "$0" -- "$@" # -*-emacs-lisp-*-
;; (pop argv) ; Remove the "--" argument
;; ;; (setq debug-on-error t) ; if a backtrace is wanted
;; (defun stdout (msg &optional args) (princ (format msg args)))
;; (defun stderr (msg &optional args) (princ (format msg args)
;;                                           #'external-debugging-output))
;; ;; [script body here]
;; Always exit explicitly. This returns the desired exit
;; status, and also avoids the need to (setq argv nil).
;; (kill-emacs 0)

;; Processing with STDIN and STDOUT via --script:
;; https://stackoverflow.com/questions/2879746/#2906967
;;
;; #!/bin/sh
;; ":"; exec emacs -Q --script "$0" -- "$@" # -*-emacs-lisp-*-
;; (pop argv) ; Remove the "--" argument
;; (setq debug-on-error t) ; if a backtrace is wanted
;; (defun stdout (msg &optional args) (princ (format msg args)))
;; (defun stderr (msg &optional args) (princ (format msg args)
;;                                           #'external-debugging-output))
;; (defun process (string)
;;   "Reverse STRING."
;;   (concat (nreverse (string-to-list string))))
;;
;; (condition-case nil
;;     (let (line)
;;       (while (setq line (read-from-minibuffer ""))
;;         (stdout "%s\n" (process line))))
;;   (error nil))
;;
;; ;; Always exit explicitly. This returns the desired exit
;; ;; status, and also avoids the need to (setq argv nil).
;; (kill-emacs 0)

Emacs aside, the only other elisp interpreter/compiler I'm aware of is Guile. If you're keen on general coding in elisp, that should be worth a look (especially if performance is a concern).