How do you 'redo' changes after 'undo' with Emacs?

This article says that "Emacs has redo because you can reverse direction while undoing, thereby undoing the undo".

What does this mean? How can a user 'redo' with Emacs?

Solution 1:

Short version: by undoing the undo. If you undo, and then do a non-editing command such as C-f, then the next undo will undo the undo, resulting in a redo.

Longer version:

You can think of undo as operating on a stack of operations. If you perform some command (even a navigation command such as C-f) after a sequence of undo operations, all the undos are pushed on to the operation stack. So the next undo undoes the last command. Suppose you do have an operation sequence that looks like this:

1. Insert "foo"
2. Insert "bar"
3. Insert "I love spam"

Now, you undo. It undoes the last action, resulting in the following list:

1. Insert "foo"
2. Insert "bar"

If you do something other than undo at this point - say, C-f, the operation stack looks like this:

1. Insert "foo"
2. Insert "bar"
3. Insert "I love spam"
4. Undo insert "I love spam"

Now, when you undo, the first thing that is undone is the undo. Resulting in your original stack (and document state):

1. Insert "foo"
2. Insert "bar"
3. Insert "I love spam"

If you do a modifying command to break the undo sequence, that command is added after the undo and is thus the first thing to be undone afterwards. Suppose you backspaced over "bar" instead of hitting C-f. Then you would have had

1. Insert "foo"
2. Insert "bar"
3. Insert "I love spam"
4. Undo insert "I love spam"
5. Delete "bar"

This adding/re-adding happens ad infinitum. It takes a little getting used to, but it really does give Emacs a highly flexible and powerful undo/redo mechanism.

Solution 2:

To undo: C-_

To redo after a undo: C-g C-_

Type multiple times on C-_ to redo what have been undone by C-_ To redo an emacs command multiple times, execute your command then type C-xz and then type many times on z key to repeat the command (interesting when you want to execute multiple times a macro)

Solution 3:

• To undo once: C-/
• To undo twice: C-/ C-/

• To redo once, immediately after undoing: C-g C-/
• To redo twice, immediately after undoing: C-g C-/ C-/. Note that C-g is not repeated.

• To undo immediately again, once: C-g C-/
• To undo immediately again, twice: C-g C-/ C-/

• To redo again, the same…

If you have pressed any keys (whether typing characters or just moving the cursor) since your last undo command, there is no need to type C-g before your next undo/redo. C-g is just a safe key to hit that does nothing on its own, but counts as a non-undo key to signal the end of your undo sequence. Pressing another command such as C-f would work too; it’s just that it would move the cursor from where you had it.

If you hit C-g or another command when you didn’t mean to, and you are now undoing in the wrong direction, simply hit C-g to reverse your direction again. You will have to undo all the way through your accidental redos and undos before you get to the undos you want, but if you just keep hitting C-/, you will eventually reach the state you want. In fact, every state the buffer has ever been in is reachable, if you hit C-g once and then press C-/ enough times.

Alternative shortcuts for undo, other than C-/, are C-_, C-x u, and M-x undo.

See Undo in the Emacs Manual for more details on Emacs’s undo system.