Vim documentation: usr_32

*usr_32.txt*	For Vim version 8.1.  Last change: 2010 Jul 20

		     VIM USER MANUAL - by Bram Moolenaar

			      The 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.

|32.1|	Undo up to a file write
|32.2|	Numbering changes
|32.3|	Jumping around the tree
|32.4|	Time travelling

     Next chapter: |usr_40.txt|  Make new commands
 Previous chapter: |usr_31.txt|  Exploiting the GUI
Table of contents: |usr_toc.txt|

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*32.1*	Undo 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|.

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*32.2*	Numbering changes

In section |02.5| 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.

==============================================================================

*32.3*	Jumping 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.

==============================================================================

*32.4*	Time 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()

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Next chapter: |usr_40.txt|  Make new commands

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