Re-open *scratch* buffer in Emacs?

GNU Emacs default bindings:

C-xb *scratch* RET

or, more verbosely

M-x switch-to-buffer *scratch* RET

The *scratch* buffer is the buffer selected upon startup, and has the major mode Lisp Interaction. Note: the mode for the *scratch* buffer is controlled by the variable initial-major-mode.

In general you can create as many "scratch" buffers as you want, and name them however you choose.

C-xb NAME RET

switches to a buffer NAME, creating it if it doesn't exist. A new buffer is not associated with a file on disk until you use C-xC-w (or M-x write-file RET) to choose a file where it should be saved.

M-x text-mode RET

changes the current buffer's major mode to Text mode. To find all the modes available (that is, without requiring any new packages), you can get a list by typing:

M-x apropos-command -mode$ RET

I add following in my .emacs:

;; bury *scratch* buffer instead of kill it
(defadvice kill-buffer (around kill-buffer-around-advice activate)
  (let ((buffer-to-kill (ad-get-arg 0)))
    (if (equal buffer-to-kill "*scratch*")
        (bury-buffer)
      ad-do-it)))

If I don't want to see scratch buffer I press C-x C-k , but it doesn't kill it, just place in the end of buffer list, so then I need it next time I don't have to create new one.

C-x b *scratch* RET y RET with iswitchb-mode enabled.

Just C-x b *scratch* RET otherwise.

I found this years ago when I first started using emacs; I have no idea where now but it has always had a home in my personal .el files. It does pop up in google searches.

;;; Prevent killing the *scratch* buffer -- source forgotten
;;;----------------------------------------------------------------------
;;; Make the *scratch* buffer behave like "The thing your aunt gave you,
;;; which you don't know what is."
(save-excursion
  (set-buffer (get-buffer-create "*scratch*"))
  (make-local-variable 'kill-buffer-query-functions)
  (add-hook 'kill-buffer-query-functions 'kill-scratch-buffer))

(defun kill-scratch-buffer ()
  ;; The next line is just in case someone calls this manually
  (set-buffer (get-buffer-create "*scratch*"))

  ;; Kill the current (*scratch*) buffer
  (remove-hook 'kill-buffer-query-functions 'kill-scratch-buffer)
  (kill-buffer (current-buffer))

  ;; Make a brand new *scratch* buffer
  (set-buffer (get-buffer-create "*scratch*"))
  (lisp-interaction-mode)
  (make-local-variable 'kill-buffer-query-functions)
  (add-hook 'kill-buffer-query-functions 'kill-scratch-buffer)

  ;; Since we killed it, don't let caller do that.
  nil)
;;;----------------------------------------------------------------------

I used to use dwj's solution, and I was quite happy about it, until the day I realized that it failed when you actually rename the scratch buffer (for example by saving it).

Then I adopted this, which works well for me :

  (run-with-idle-timer 1 t
    '(lambda () (get-buffer-create "*scratch*")))

Like the docstring says, this function will:

Switch to the scratch buffer. If the buffer doesn't exist create it and write the initial message into it."

This will bring a new scratch buffer up which looks like the initial scratch buffer.

(defun switch-buffer-scratch ()
  "Switch to the scratch buffer. If the buffer doesn't exist,
create it and write the initial message into it."
  (interactive)
  (let* ((scratch-buffer-name "*scratch*")
         (scratch-buffer (get-buffer scratch-buffer-name)))
    (unless scratch-buffer
      (setq scratch-buffer (get-buffer-create scratch-buffer-name))
      (with-current-buffer scratch-buffer
        (lisp-interaction-mode)
        (insert initial-scratch-message)))
    (switch-to-buffer scratch-buffer)))

(global-set-key "\C-cbs" 'switch-buffer-scratch)

This is what I use - I have this bound to a convenient keystroke. It sends you to the *scratch* buffer, regardless of whether or not it already exists, and sets it to be in lisp-interaction-mode

(defun eme-goto-scratch () 
  "this sends you to the scratch buffer"
  (interactive)
  (let ((eme-scratch-buffer (get-buffer-create "*scratch*")))
    (switch-to-buffer eme-scratch-buffer)
    (lisp-interaction-mode)))

To add to the accepted answer, if you have ILO mode on (and it is autocompleting after C-x b, thus not letting you write *scratch*), then try:

C-xb C-b*scratch* RET

C-x b C-b *scratch* RET

C-xb and then type *scratch* ↩︎

to create a new buffer which is in lisp interaction mode also.