Boilerplate to write a command line script in emacs lisp

run-with-emacs

:;exec emacs --no-init-file --no-site-lisp -script "$0" -- "$@" # -*- mode:emacs-lisp -*-
(defun main ()
  (require 'cl-lib)
  (let ((script-name (nth 2 command-line-args))
        (args (cdr command-line-args-left)))
    ;; assert: ARGS now is a possibly empty list of command line args to the script

    ;; check for valid arguments here
    (when (not args)
      (princ (format "usage: %s PATH_TO_FILE" script-name))
      (kill-emacs))

    ;; start real work here

    (princ (format "Hello world. Argument list: %S\n" args))

    ;; ;; example of creating a file by modifying
    ;; (let* ((orig-filename (nth 0 args))
    ;;        (new-filename (format "%s.fixed" orig-filename)))
    ;;   (find-file new-filename)
    ;;   (insert-file-contents orig-filename)

    ;;   ;; do buffer-transforming work here
    ;;   (let ((replaced (replace-regexp-in-region  "[, α-ωά-ώ]+\n\n[, Ά-ΏΑ-Ω]+"
    ;;                                              "CHAPTERHERE\n\1")))
    ;;     (princ (format "Replaced %s instances\n" replaced)))
    ;;   (save-buffer))
    ))

(main)

;; Q: Why does the initial line work?
;;
;; The file is valid elisp, because : is a no-op as a self-evaluating
;; value, and ; comments out the rest of the line.
;;
;; It's also valid sh, since : triggers interpretation, ; is sh no-op as
;; the command delimiter, and "exec" hands over process control, which
;; stops sh from reading the remaining lines.
;;
;; 
;; notes on this: 
;; - https://www.emacswiki.org/emacs/BatchMode 
;; - https://www.emacswiki.org/emacs/EmacsScripts
;; - https://emacs.stackexchange.com/a/10132/9190