Is there a keybind or a way of undoing each of ediff A-B change? I often want to revert the previous modification.

3 Answers 3


ediff-mode has built-in bindings to apply and revert diff hunks.

Let's say you are running ediff between files/buffers A and B.

  • To copy A's region to B, press a
  • To undo that, i.e. to restore the original region in buffer B, do rb


  • To copy B's region to A, press b
  • To undo that, i.e. to restore the original region in buffer A, do ra

While the ediff is in progress, you can hit ? to know more bindings.

      Move around      |      Toggle features      |        Manipulate
  p,DEL -previous diff |     | -vert/horiz split   |a/b -copy A/B's region to B/A
  n,SPC -next diff     |     h -highlighting       | rx -restore buf X's old diff
      j -jump to diff  |     @ -auto-refinement    |  * -refine current region
     gx -goto X's point|    ## -ignore whitespace  |  ! -update diff regions
    C-l -recenter      |    #c -ignore case        |
    v/V -scroll up/dn  | #f/#h -focus/hide regions | wx -save buf X
    </> -scroll lt/rt  |     X -read-only in buf X | wd -save diff output
      ~ -swap variants |     m -wide display       |
      R -show registry |     = -compare regions    |  M   -show session group
      D -diff output   |     E -browse Ediff manual|  G   -send bug report
      i -status info   |     ? -help off           |  z/q -suspend/quit
  For help on a specific command:  Click Button 2 over it; or
                                   Put the cursor over it and type RET.
  • This is exactly what I wanted! (I want to vote but couldn't due to the lower-than-15-reputation limits) Commented Jun 9, 2015 at 16:21

Select the buffer that was changed by the last modification (e.g. put the cursor there), and then hit C-_ (undo).

Undo is per buffer. Each Ediff change affects one buffer. Go to that buffer and use undo.


I managed to solve like below, thanks to Drew's answer.

;; use undo-tree.el
(defun my-ediff-undo-A ()
  (save-window-excursion (with-selected-window ediff-window-A (undo-tree-undo))))
(defun my-ediff-undo-B ()
  (save-window-excursion (with-selected-window ediff-window-B (undo-tree-undo))))
(defun my-ediff-redo-A ()
  (save-window-excursion (with-selected-window ediff-window-A (undo-tree-redo))))
(defun my-ediff-redo-B ()
  (save-window-excursion (with-selected-window ediff-window-B (undo-tree-redo))))

(defadvice ediff-setup-keymap (around my-ediff-undo activate)
  (define-key ediff-mode-map (kbd "C-a") 'my-ediff-undo-A)
  (define-key ediff-mode-map (kbd "C-b") 'my-ediff-undo-B)
  (define-key ediff-mode-map (kbd "M-a") 'my-ediff-redo-A)
  (define-key ediff-mode-map (kbd "M-b") 'my-ediff-redo-B))

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