Question

Is there a builtin command to clear shell while using shell in emacs?

If not, is there an elisp function to achieve the same?

Answer 1

Update February 2015

Just noticed that Emacs now (version 25+) has the command comint-clear-buffer, bound to C-c M-o by default, that does what we need here, and probably is preferable to the answers I originally posted below.

Options to consider:

1. C-l will recenter the buffer. Pressing it repeatedly cycles the buffer, so that point appears at the top, middle, or bottom of the buffer. When it stops at the top, the buffer looks like it’s been cleared, although all the text is still there, out of view.

2. C-x h marks the whole buffer, after which C-w kills it. This kills the last prompt as well, but after you enter the next command you get your prompt back.

3. You can also use erase-buffer, which isn’t bound to a key by default, but it’s easily done (you can also use M-x erase-buffer:

    (defun my-shell-hook ()
      (local-set-key "\C-cl" 'erase-buffer))

    (add-hook 'shell-mode-hook 'my-shell-hook)

That binds it to C-c l; you can pick what you like.

4. A quick fix to re-create your prompt after clearing is possible:

    (defun my-clear ()
      (interactive)
      (erase-buffer)
      (comint-send-input))

    (defun my-shell-hook ()
      (local-set-key "\C-cl" 'my-clear))

    (add-hook 'shell-mode-hook 'my-shell-hook)

After you’ve been using emacs for a while, marking and killing regions becomes natural, so you might find the first option is enough. If not, the last option is closest to what you want.

EDIT: just found this on the emacs wiki, it’s better than my option 4:

(defun my-clear ()
  (interactive)
  (let ((comint-buffer-maximum-size 0))
    (comint-truncate-buffer)))