32The undo tree

Vim provides multi-level undo. If you undo a few changes and then make a new change you create a branch in the undo tree. This text is about moving through the branches.

    Table of contents

  1. Undo up to a file write
  2. Numbering changes
  3. Jumping around the tree
  4. Time travelling

32.1Undo up to a file write

Sometimes you make several changes, and then discover you want to go back to when you have last written the file. You can do that with this command:

:earlier 1f

The f stands for file here.

You can repeat this command to go further back in the past. Or use a count different from 1 to go back faster.

If you go back too far, go forward again with:

:later 1f

Note that these commands really work in time sequence. This matters if you made changes after undoing some changes. It's explained in the next section.

Also note that we are talking about text writes here. For writing the undo information in a file see undo‑persistence.

32.2Numbering changes

In section “Undo and Redo” we only discussed one line of undo/redo. But it is also possible to branch off. This happens when you undo a few changes and then make a new change. The new changes become a branch in the undo tree.

Let's start with the text one. The first change to make is to append " too". And then move to the first 'o' and change it into 'w'. We then have two changes, numbered 1 and 2, and three states of the text:

	one
	 |
      change 1
	 |
      one too
	 |
      change 2
	 |
      one two

If we now undo one change, back to "one too", and change one to me we create a branch in the undo tree:

	one
	 |
      change 1
	 |
      one too
      /     \
 change 2  change 3
    |	      |
 one two    me too

You can now use the u command to undo. If you do this twice you get to one. Use CTRL‑R to redo, and you will go to "one too". One more CTRL‑R takes you to "me too". Thus undo and redo go up and down in the tree, using the branch that was last used.

What matters here is the order in which the changes are made. Undo and redo are not considered changes in this context. After each change you have a new state of the text.

Note that only the changes are numbered, the text shown in the tree above has no identifier. They are mostly referred to by the number of the change above it. But sometimes by the number of one of the changes below it, especially when moving up in the tree, so that you know which change was just undone.

32.3Jumping around the tree

So how do you get to "one two" now? You can use this command:

:undo 2

The text is now "one two", you are below change 2. You can use the :undo command to jump to below any change in the tree.

Now make another change: change one to not:

	one
	 |
      change 1
	 |
      one too
      /     \
 change 2  change 3
    |	      |
 one two    me too
    |
 change 4
    |
 not two

Now you change your mind and want to go back to "me too". Use the g‑ command. This moves back in time. Thus it doesn't walk the tree upwards or downwards, but goes to the change made before.

You can repeat g‑ and you will see the text change:

me too
one two
one too
one

Use g+ to move forward in time:

one
one too
one two
me too
not two

Using :undo is useful if you know what change you want to jump to. g‑ and g+ are useful if you don't know exactly what the change number is.

You can type a count before g‑ and g+ to repeat them.

32.4Time travelling

When you have been working on text for a while the tree grows to become big. Then you may want to go to the text of some minutes ago.

To see what branches there are in the undo tree use this command:

:undolist
number changes  time ~
     3       2  16 seconds ago
     4       3  5 seconds ago

Here you can see the number of the leaves in each branch and when the change was made. Assuming we are below change 4, at "not two", you can go back ten seconds with this command:

:earlier 10s

Depending on how much time you took for the changes you end up at a certain position in the tree. The :earlier command argument can be m for minutes, h for hours and d for days. To go all the way back use a big number:

:earlier 100d

To travel forward in time again use the :later command:

:later 1m

The arguments are s, m and h, just like with :earlier.

If you want even more details, or want to manipulate the information, you can use the undotree() function. To see what it returns:

:echo undotree()