How to replace the default contents of the scratch buffer with the contents of a file (if it exists)?

Question

I would like emacs to check for a ~/emacs.d/scratch.txt and use it's contents instead of the default message when emacs starts.

How can this be done?

Answer 1

initial-buffer-choice allows to specify a path to a file or directory:

(let ((filename "~/.emacs.d/startup.txt"))
  (when (file-exists-p filename)
    (setq initial-buffer-choice filename)))

Answer 2

This will do the job.

(let ((filename (concat user-emacs-directory "scratch.txt")))
  (when (file-exists-p filename)
    (let ((scratch-buf (get-buffer "*scratch*")))
      (when scratch-buf
        (with-current-buffer scratch-buf
          (erase-buffer)
          (insert-file-contents filename))))))

Answer 3

I would use initial-scratch-message.

(let ((file "~/.emacs.d/scratch.txt"))
  (when (file-exists-p file)
    (setq initial-scratch-message
      (with-temp-buffer
        (insert-file-contents file)
        (buffer-string)))))

Answer 4

This can be done using initial-buffer-choice,

While initial-buffer-choice can be set to a filename, this will load the file as well as any files passed via the command line (splitting the window or not even showing the buffer depending on your setup).
So reading file data into *scratch* buffer has the advantage that exact behavior is preserved, just replacing the text.

This example:

• Only runs when the user starts without loading a file.

• Loads in a text file into the startup buffer.

• Users a default startup.txt, optionally taking a user defined startup file.

• Sets the mode based on the filename, so users can pass in startup.org for an org-mode buffer.

• Adds a short commented line at the top of the file, eg:

  # Emacs: 28.0, time: 0.93, packages: 58

• When no startup file is found, the name of the file to create is referenced.

;; Load startup text when available.
;;
;; Example usage:
;;
;;   (my-scratch-buffer-from-file)
;;
;; Or if you like to use an org-mode scratch buffer,
;; an option file path can be passed in.
;; The file extension is used to set the mode:
;;
;;   (my-scratch-buffer-from-file (concat user-emacs-directory "scratch.org"))
;;

(defvar my-scratch-buffer-from-file--value nil)
(defun my-scratch-buffer-from-file (&optional scratch-file)
  (setq inhibit-startup-screen t)
  (setq initial-scratch-message nil)
  (when scratch-file
    (setq my-scratch-buffer-from-file--value scratch-file))

  (setq
   initial-buffer-choice
   (lambda ()
     (if (buffer-file-name)
         (current-buffer) ;; leave as-is
       (let ((original-buffer (current-buffer))
             (filename
              (or my-scratch-buffer-from-file--value
                  (concat user-emacs-directory "scratch.txt")))
             ;; Not essential, just gives some handy startup info.
             (startup-info
              (format
               "Emacs: %d.%d, time: %.2f, packages: %d"
               emacs-major-version
               emacs-minor-version
               (float-time (time-subtract after-init-time before-init-time))
               (length package-activated-list))))
         (with-current-buffer (get-buffer-create "*scratch*")
           ;; Don't track undo.
           (buffer-disable-undo)

           ;; Set the mode based on the filename, users may use filenames that infer modes.
           (condition-case err
               (let ((buffer-file-name filename))
                 (set-auto-mode t))
             (error (message "Unable to activate mode: %s" err)))

           ;; Use the comment character set by the mode where possible.
           (let ((comment-start-or-empty
                  (if comment-start
                      ;; Ensure one trailing space (some comments include space).
                      (concat
                       (replace-regexp-in-string "[[:blank:]]*$" "" comment-start)
                       " ")
                    "")))
             (if (file-exists-p filename)
                 (insert-file-contents filename)
               (insert
                comment-start-or-empty
                (format "Scratch buffer, create '%s' to replace this text on startup."
                        filename))
               (goto-char (point-min)))
             ;; Add some startup info above the static text.
             (insert comment-start-or-empty startup-info "\n\n"))
           (buffer-enable-undo)
           (set-buffer original-buffer)))))))

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Others might suggest how this can be done better, it seems to work well enough though.