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Edit File : undo.txt \| Size : 16.15 KB
undo.txt For Vim version 8.0. Last change: 2014 May 24 VIM REFERENCE MANUAL by Bram Moolenaar Undo and redo undo-redo The basics are explained in section \|02.5\| of the user manual. 1. Undo and redo commands \|undo-commands\| 2. Two ways of undo \|undo-two-ways\| 3. Undo blocks \|undo-blocks\| 4. Undo branches \|undo-branches\| 5. Undo persistence \|undo-persistence\| 6. Remarks about undo \|undo-remarks\| ============================================================================== 1. Undo and redo commands undo-commands <Undo> or undo <Undo> u u Undo [count] changes. {Vi: only one level} :u :un :undo :u[ndo] Undo one change. {Vi: only one level} E830 :u[ndo] {N} Jump to after change number {N}. See \|undo-branches\| for the meaning of {N}. {not in Vi} CTRL-R CTRL-R Redo [count] changes which were undone. {Vi: redraw screen} :red :redo redo :red[o] Redo one change which was undone. {Vi: no redo} U U Undo all latest changes on one line, the line where the latest change was made. \|U\| itself also counts as a change, and thus \|U\| undoes a previous \|U\|. {Vi: while not moved off of the last modified line} The last changes are remembered. You can use the undo and redo commands above to revert the text to how it was before each change. You can also apply the changes again, getting back the text before the undo. The "U" command is treated by undo/redo just like any other command. Thus a "u" command undoes a "U" command and a 'CTRL-R' command redoes it again. When mixing "U", "u" and 'CTRL-R' you will notice that the "U" command will restore the situation of a line to before the previous "U" command. This may be confusing. Try it out to get used to it. The "U" command will always mark the buffer as changed. When "U" changes the buffer back to how it was without changes, it is still considered changed. Use "u" to undo changes until the buffer becomes unchanged. ============================================================================== 2. Two ways of undo undo-two-ways How undo and redo commands work depends on the 'u' flag in 'cpoptions'. There is the Vim way ('u' excluded) and the Vi-compatible way ('u' included). In the Vim way, "uu" undoes two changes. In the Vi-compatible way, "uu" does nothing (undoes an undo). 'u' excluded, the Vim way: You can go back in time with the undo command. You can then go forward again with the redo command. If you make a new change after the undo command, the redo will not be possible anymore. 'u' included, the Vi-compatible way: The undo command undoes the previous change, and also the previous undo command. The redo command repeats the previous undo command. It does NOT repeat a change command, use "." for that. Examples Vim way Vi-compatible way ~ "uu" two times undo no-op "u CTRL-R" no-op two times undo Rationale: Nvi uses the "." command instead of CTRL-R. Unfortunately, this is not Vi compatible. For example "dwdwu." in Vi deletes two words, in Nvi it does nothing. ============================================================================== 3. Undo blocks undo-blocks One undo command normally undoes a typed command, no matter how many changes that command makes. This sequence of undo-able changes forms an undo block. Thus if the typed key(s) call a function, all the commands in the function are undone together. If you want to write a function or script that doesn't create a new undoable change but joins in with the previous change use this command: :undoj :undojoin E790 :undoj[oin] Join further changes with the previous undo block. Warning: Use with care, it may prevent the user from properly undoing changes. Don't use this after undo or redo. {not in Vi} This is most useful when you need to prompt the user halfway through a change. For example in a function that calls \|getchar()\|. Do make sure that there was a related change before this that you must join with. This doesn't work by itself, because the next key press will start a new change again. But you can do something like this: > :undojoin \| delete After this an "u" command will undo the delete command and the previous change. To do the opposite, break a change into two undo blocks, in Insert mode use CTRL-G u. This is useful if you want an insert command to be undoable in parts. E.g., for each sentence. \|i_CTRL-G_u\| Setting the value of 'undolevels' also breaks undo. Even when the new value is equal to the old value. ============================================================================== 4. Undo branches undo-branches undo-tree Above 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 undone changes become a branch. You can go to that branch with the following commands. This is explained in the user manual: \|usr_32.txt\|. :undol :undolist :undol[ist] List the leafs in the tree of changes. Example: number changes when saved ~ 88 88 2010/01/04 14:25:53 108 107 08/07 12:47:51 136 46 13:33:01 7 166 164 3 seconds ago The "number" column is the change number. This number continuously increases and can be used to identify a specific undo-able change, see \|:undo\|. The "changes" column is the number of changes to this leaf from the root of the tree. The "when" column is the date and time when this change was made. The four possible formats are: N seconds ago HH:MM:SS hour, minute, seconds MM/DD HH:MM:SS idem, with month and day YYYY/MM/DD HH:MM:SS idem, with year The "saved" column specifies, if this change was written to disk and which file write it was. This can be used with the \|:later\| and \|:earlier\| commands. For more details use the \|undotree()\| function. g- g- Go to older text state. With a count repeat that many times. {not in Vi} :ea :earlier :earlier {count} Go to older text state {count} times. :earlier {N}s Go to older text state about {N} seconds before. :earlier {N}m Go to older text state about {N} minutes before. :earlier {N}h Go to older text state about {N} hours before. :earlier {N}d Go to older text state about {N} days before. :earlier {N}f Go to older text state {N} file writes before. When changes were made since the last write ":earlier 1f" will revert the text to the state when it was written. Otherwise it will go to the write before that. When at the state of the first file write, or when the file was not written, ":earlier 1f" will go to before the first change. g+ g+ Go to newer text state. With a count repeat that many times. {not in Vi} :lat :later :later {count} Go to newer text state {count} times. :later {N}s Go to newer text state about {N} seconds later. :later {N}m Go to newer text state about {N} minutes later. :later {N}h Go to newer text state about {N} hours later. :later {N}d Go to newer text state about {N} days later. :later {N}f Go to newer text state {N} file writes later. When at the state of the last file write, ":later 1f" will go to the newest text state. Note that text states will become unreachable when undo information is cleared for 'undolevels'. Don't be surprised when moving through time shows multiple changes to take place at a time. This happens when moving through the undo tree and then making a new change. EXAMPLE Start with this text: one two three ~ Delete the first word by pressing "x" three times: ne two three ~ e two three ~ two three ~ Now undo that by pressing "u" three times: e two three ~ ne two three ~ one two three ~ Delete the second word by pressing "x" three times: one wo three ~ one o three ~ one three ~ Now undo that by using "g-" three times: one o three ~ one wo three ~ two three ~ You are now back in the first undo branch, after deleting "one". Repeating "g-" will now bring you back to the original text: e two three ~ ne two three ~ one two three ~ Jump to the last change with ":later 1h": one three ~ And back to the start again with ":earlier 1h": one two three ~ Note that using "u" and CTRL-R will not get you to all possible text states while repeating "g-" and "g+" does. ============================================================================== 5. Undo persistence undo-persistence persistent-undo When unloading a buffer Vim normally destroys the tree of undos created for that buffer. By setting the 'undofile' option, Vim will automatically save your undo history when you write a file and restore undo history when you edit the file again. The 'undofile' option is checked after writing a file, before the BufWritePost autocommands. If you want to control what files to write undo information for, you can use a BufWritePre autocommand: > au BufWritePre /tmp/* setlocal noundofile Vim saves undo trees in a separate undo file, one for each edited file, using a simple scheme that maps filesystem paths directly to undo files. Vim will detect if an undo file is no longer synchronized with the file it was written for (with a hash of the file contents) and ignore it when the file was changed after the undo file was written, to prevent corruption. An undo file is also ignored if its owner differs from the owner of the edited file, except when the owner of the undo file is the current user. Set 'verbose' to get a message about that when opening a file. Undo files are normally saved in the same directory as the file. This can be changed with the 'undodir' option. When the file is encrypted, the text in the undo file is also crypted. The same key and method is used. \|encryption\| You can also save and restore undo histories by using ":wundo" and ":rundo" respectively: :wundo :rundo :wundo[!] {file} Write undo history to {file}. When {file} exists and it does not look like an undo file (the magic number at the start of the file is wrong), then this fails, unless the ! was added. If it exists and does look like an undo file it is overwritten. If there is no undo-history, nothing will be written. Implementation detail: Overwriting happens by first deleting the existing file and then creating a new file with the same name. So it is not possible to overwrite an existing undofile in a write-protected directory. {not in Vi} :rundo {file} Read undo history from {file}. {not in Vi} You can use these in autocommands to explicitly specify the name of the history file. E.g.: > au BufReadPost * call ReadUndo() au BufWritePost * call WriteUndo() func ReadUndo() if filereadable(expand('%:h'). '/UNDO/' . expand('%:t')) rundo %:h/UNDO/%:t endif endfunc func WriteUndo() let dirname = expand('%:h') . '/UNDO' if !isdirectory(dirname) call mkdir(dirname) endif wundo %:h/UNDO/%:t endfunc You should keep 'undofile' off, otherwise you end up with two undo files for every write. You can use the \|undofile()\| function to find out the file name that Vim would use. Note that while reading/writing files and 'undofile' is set most errors will be silent, unless 'verbose' is set. With :wundo and :rundo you will get more error messages, e.g., when the file cannot be read or written. NOTE: undo files are never deleted by Vim. You need to delete them yourself. Reading an existing undo file may fail for several reasons: E822 It cannot be opened, because the file permissions don't allow it. E823 The magic number at the start of the file doesn't match. This usually means it is not an undo file. E824 The version number of the undo file indicates that it's written by a newer version of Vim. You need that newer version to open it. Don't write the buffer if you want to keep the undo info in the file. "File contents changed, cannot use undo info" The file text differs from when the undo file was written. This means the undo file cannot be used, it would corrupt the text. This also happens when 'encoding' differs from when the undo file was written. E825 The undo file does not contain valid contents and cannot be used. E826 The undo file is encrypted but decryption failed. E827 The undo file is encrypted but this version of Vim does not support encryption. Open the file with another Vim. E832 The undo file is encrypted but 'key' is not set, the text file is not encrypted. This would happen if the text file was written by Vim encrypted at first, and later overwritten by not encrypted text. You probably want to delete this undo file. "Not reading undo file, owner differs" The undo file is owned by someone else than the owner of the text file. For safety the undo file is not used. Writing an undo file may fail for these reasons: E828 The file to be written cannot be created. Perhaps you do not have write permissions in the directory. "Cannot write undo file in any directory in 'undodir'" None of the directories in 'undodir' can be used. "Will not overwrite with undo file, cannot read" A file exists with the name of the undo file to be written, but it cannot be read. You may want to delete this file or rename it. "Will not overwrite, this is not an undo file" A file exists with the name of the undo file to be written, but it does not start with the right magic number. You may want to delete this file or rename it. "Skipping undo file write, nothing to undo" There is no undo information to be written, nothing has been changed or 'undolevels' is negative. E829 An error occurred while writing the undo file. You may want to try again. ============================================================================== 6. Remarks about undo undo-remarks The number of changes that are remembered is set with the 'undolevels' option. If it is zero, the Vi-compatible way is always used. If it is negative no undo is possible. Use this if you are running out of memory. clear-undo When you set 'undolevels' to -1 the undo information is not immediately cleared, this happens at the next change. To force clearing the undo information you can use these commands: > :let old_undolevels = &undolevels :set undolevels=-1 :exe "normal a \<BS>\<Esc>" :let &undolevels = old_undolevels :unlet old_undolevels Marks for the buffer ('a to 'z) are also saved and restored, together with the text. {Vi does this a little bit different} When all changes have been undone, the buffer is not considered to be changed. It is then possible to exit Vim with ":q" instead of ":q!" {not in Vi}. Note that this is relative to the last write of the file. Typing "u" after ":w" actually changes the buffer, compared to what was written, so the buffer is considered changed then. When manual \|folding\| is being used, the folds are not saved and restored. Only changes completely within a fold will keep the fold as it was, because the first and last line of the fold don't change. The numbered registers can also be used for undoing deletes. Each time you delete text, it is put into register "1. The contents of register "1 are shifted to "2, etc. The contents of register "9 are lost. You can now get back the most recent deleted text with the put command: '"1P'. (also, if the deleted text was the result of the last delete or copy operation, 'P' or 'p' also works as this puts the contents of the unnamed register). You can get back the text of three deletes ago with '"3P'. redo-register If you want to get back more than one part of deleted text, you can use a special feature of the repeat command ".". It will increase the number of the register used. So if you first do ""1P", the following "." will result in a '"2P'. Repeating this will result in all numbered registers being inserted. Example: If you deleted text with 'dd....' it can be restored with '"1P....'. If you don't know in which register the deleted text is, you can use the :display command. An alternative is to try the first register with '"1P', and if it is not what you want do 'u.'. This will remove the contents of the first put, and repeat the put command for the second register. Repeat the 'u.' until you got what you want. vim:tw=78:ts=8:ft=help:norl: Back

Edit File : undo.txt | Size : 16.15 KB

*undo.txt*      For Vim version 8.0.  Last change: 2014 May 24

VIM REFERENCE MANUAL    by Bram Moolenaar

Undo and redo						*undo-redo*

The basics are explained in section |02.5| of the user manual.

==============================================================================
1. Undo and redo commands				*undo-commands*

<Undo>		or					*undo* *<Undo>* *u*
u			Undo [count] changes.  {Vi: only one level}

*:u* *:un* *:undo*
:u[ndo]			Undo one change.  {Vi: only one level}
								*E830*
:u[ndo] {N}		Jump to after change number {N}.  See |undo-branches|
			for the meaning of {N}.  {not in Vi}

*CTRL-R*
CTRL-R			Redo [count] changes which were undone.  {Vi: redraw
			screen}

*:red* *:redo* *redo*
:red[o]			Redo one change which was undone.  {Vi: no redo}

*U*
U			Undo all latest changes on one line, the line where
			the latest change was made. |U| itself also counts as
			a change, and thus |U| undoes a previous |U|.
			{Vi: while not moved off of the last modified line}

The last changes are remembered.  You can use the undo and redo commands above
to revert the text to how it was before each change.  You can also apply the
changes again, getting back the text before the undo.

The "U" command is treated by undo/redo just like any other command.  Thus a
"u" command undoes a "U" command and a 'CTRL-R' command redoes it again.  When
mixing "U", "u" and 'CTRL-R' you will notice that the "U" command will
restore the situation of a line to before the previous "U" command.  This may
be confusing.  Try it out to get used to it.
The "U" command will always mark the buffer as changed.  When "U" changes the
buffer back to how it was without changes, it is still considered changed.
Use "u" to undo changes until the buffer becomes unchanged.

==============================================================================
2. Two ways of undo					*undo-two-ways*

How undo and redo commands work depends on the 'u' flag in 'cpoptions'.
There is the Vim way ('u' excluded) and the Vi-compatible way ('u' included).
In the Vim way, "uu" undoes two changes.  In the Vi-compatible way, "uu" does
nothing (undoes an undo).

'u' excluded, the Vim way:
You can go back in time with the undo command.  You can then go forward again
with the redo command.  If you make a new change after the undo command,
the redo will not be possible anymore.

'u' included, the Vi-compatible way:
The undo command undoes the previous change, and also the previous undo command.
The redo command repeats the previous undo command.  It does NOT repeat a
change command, use "." for that.

Examples	Vim way			Vi-compatible way	~
"uu"		two times undo		no-op
"u CTRL-R"	no-op			two times undo

Rationale:  Nvi uses the "." command instead of CTRL-R.  Unfortunately, this
	    is not Vi compatible.  For example "dwdwu." in Vi deletes two
	    words, in Nvi it does nothing.

==============================================================================
3. Undo blocks						*undo-blocks*

One undo command normally undoes a typed command, no matter how many changes
that command makes.  This sequence of undo-able changes forms an undo block.
Thus if the typed key(s) call a function, all the commands in the function are
undone together.

If you want to write a function or script that doesn't create a new undoable
change but joins in with the previous change use this command:

*:undoj* *:undojoin* *E790*
:undoj[oin]		Join further changes with the previous undo block.
			Warning: Use with care, it may prevent the user from
			properly undoing changes.  Don't use this after undo
			or redo.
			{not in Vi}

This is most useful when you need to prompt the user halfway through a change.
For example in a function that calls |getchar()|.  Do make sure that there was
a related change before this that you must join with.

This doesn't work by itself, because the next key press will start a new
change again.  But you can do something like this: >

:undojoin | delete

After this an "u" command will undo the delete command and the previous
change.

To do the opposite, break a change into two undo blocks, in Insert mode use
CTRL-G u.  This is useful if you want an insert command to be undoable in
parts.  E.g., for each sentence.  |i_CTRL-G_u|
Setting the value of 'undolevels' also breaks undo.  Even when the new value
is equal to the old value.

==============================================================================
4. Undo branches				*undo-branches* *undo-tree*

Above 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 undone changes become a branch.  You can go to that branch with
the following commands.

This is explained in the user manual: |usr_32.txt|.

*:undol* *:undolist*
:undol[ist]		List the leafs in the tree of changes.  Example:
			   number changes  when               saved ~
			       88      88  2010/01/04 14:25:53
			      108     107  08/07 12:47:51
			      136      46  13:33:01             7
			      166     164  3 seconds ago

The "number" column is the change number.  This number
			continuously increases and can be used to identify a
			specific undo-able change, see |:undo|.
			The "changes" column is the number of changes to this
			leaf from the root of the tree.
			The "when" column is the date and time when this
			change was made.  The four possible formats are:
			    N seconds ago
			    HH:MM:SS             hour, minute, seconds
			    MM/DD HH:MM:SS       idem, with month and day
			    YYYY/MM/DD HH:MM:SS  idem, with year
			The "saved" column specifies, if this change was
			written to disk and which file write it was. This can
			be used with the |:later| and |:earlier| commands.
			For more details use the |undotree()| function.

*g-*
g-			Go to older text state.  With a count repeat that many
			times.  {not in Vi}
							*:ea* *:earlier*
:earlier {count}	Go to older text state {count} times.
:earlier {N}s		Go to older text state about {N} seconds before.
:earlier {N}m		Go to older text state about {N} minutes before.
:earlier {N}h		Go to older text state about {N} hours before.
:earlier {N}d		Go to older text state about {N} days before.

:earlier {N}f		Go to older text state {N} file writes before.
			When changes were made since the last write
			":earlier 1f" will revert the text to the state when
			it was written.  Otherwise it will go to the write
			before that.
			When at the state of the first file write, or when
			the file was not written, ":earlier 1f" will go to
			before the first change.

*g+*
g+			Go to newer text state.  With a count repeat that many
			times.  {not in Vi}
							*:lat* *:later*
:later {count}		Go to newer text state {count} times.
:later {N}s		Go to newer text state about {N} seconds later.
:later {N}m		Go to newer text state about {N} minutes later.
:later {N}h		Go to newer text state about {N} hours later.
:later {N}d		Go to newer text state about {N} days later.

:later {N}f		Go to newer text state {N} file writes later.
			When at the state of the last file write, ":later 1f"
			will go to the newest text state.

Note that text states will become unreachable when undo information is cleared
for 'undolevels'.

Don't be surprised when moving through time shows multiple changes to take
place at a time.  This happens when moving through the undo tree and then
making a new change.

EXAMPLE

Start with this text:
	one two three ~

Delete the first word by pressing "x" three times:
	ne two three ~
	e two three ~
	 two three ~

Now undo that by pressing "u" three times:
	e two three ~
	ne two three ~
	one two three ~

Delete the second word by pressing "x" three times:
	one wo three ~
	one o three ~
	one  three ~

Now undo that by using "g-" three times:
	one o three ~
	one wo three ~
	 two three ~

You are now back in the first undo branch, after deleting "one".  Repeating
"g-" will now bring you back to the original text:
	e two three ~
	ne two three ~
	one two three ~

Jump to the last change with ":later 1h":
	one  three ~

And back to the start again with ":earlier 1h":
	one two three ~

Note that using "u" and CTRL-R will not get you to all possible text states
while repeating "g-" and "g+" does.

==============================================================================
5. Undo persistence		*undo-persistence* *persistent-undo*

When unloading a buffer Vim normally destroys the tree of undos created for
that buffer.  By setting the 'undofile' option, Vim will automatically save
your undo history when you write a file and restore undo history when you edit
the file again.

The 'undofile' option is checked after writing a file, before the BufWritePost
autocommands.  If you want to control what files to write undo information
for, you can use a BufWritePre autocommand: >
	au BufWritePre /tmp/* setlocal noundofile

Vim saves undo trees in a separate undo file, one for each edited file, using
a simple scheme that maps filesystem paths directly to undo files. Vim will
detect if an undo file is no longer synchronized with the file it was written
for (with a hash of the file contents) and ignore it when the file was changed
after the undo file was written, to prevent corruption.  An undo file is also
ignored if its owner differs from the owner of the edited file, except when
the owner of the undo file is the current user.  Set 'verbose' to get a
message about that when opening a file.

Undo files are normally saved in the same directory as the file.  This can be
changed with the 'undodir' option.

When the file is encrypted, the text in the undo file is also crypted.  The
same key and method is used. |encryption|

You can also save and restore undo histories by using ":wundo" and ":rundo"
respectively:
							*:wundo* *:rundo*
:wundo[!] {file}
		Write undo history to {file}.
		When {file} exists and it does not look like an undo file
		(the magic number at the start of the file is wrong), then
		this fails, unless the ! was added.
		If it exists and does look like an undo file it is
		overwritten. If there is no undo-history, nothing will be 
		written.
		Implementation detail: Overwriting happens by first deleting
		the existing file and then creating a new file with the same
		name. So it is not possible to overwrite an existing undofile
		in a write-protected directory.
		{not in Vi}

:rundo {file}	Read undo history from {file}.
		{not in Vi}

You can use these in autocommands to explicitly specify the name of the
history file.  E.g.: >

au BufReadPost * call ReadUndo()
	au BufWritePost * call WriteUndo()
	func ReadUndo()
	  if filereadable(expand('%:h'). '/UNDO/' . expand('%:t'))
	    rundo %:h/UNDO/%:t
	  endif
	endfunc
	func WriteUndo()
	  let dirname = expand('%:h') . '/UNDO'
	  if !isdirectory(dirname)
	    call mkdir(dirname)
	  endif
	  wundo %:h/UNDO/%:t
	endfunc

You should keep 'undofile' off, otherwise you end up with two undo files for
every write.

You can use the |undofile()| function to find out the file name that Vim would
use.

Note that while reading/writing files and 'undofile' is set most errors will
be silent, unless 'verbose' is set.  With :wundo and :rundo you will get more
error messages, e.g., when the file cannot be read or written.

NOTE: undo files are never deleted by Vim.  You need to delete them yourself.

Reading an existing undo file may fail for several reasons:
*E822*	It cannot be opened, because the file permissions don't allow it.
*E823*	The magic number at the start of the file doesn't match.  This usually
	means it is not an undo file.
*E824*	The version number of the undo file indicates that it's written by a
	newer version of Vim.  You need that newer version to open it.  Don't
	write the buffer if you want to keep the undo info in the file.
"File contents changed, cannot use undo info"
	The file text differs from when the undo file was written.  This means
	the undo file cannot be used, it would corrupt the text.  This also
	happens when 'encoding' differs from when the undo file was written.
*E825*  The undo file does not contain valid contents and cannot be used.
*E826*  The undo file is encrypted but decryption failed.
*E827*  The undo file is encrypted but this version of Vim does not support
	encryption.  Open the file with another Vim.
*E832*  The undo file is encrypted but 'key' is not set, the text file is not
	encrypted.  This would happen if the text file was written by Vim
	encrypted at first, and later overwritten by not encrypted text.
	You probably want to delete this undo file.
"Not reading undo file, owner differs"
	The undo file is owned by someone else than the owner of the text
	file.  For safety the undo file is not used.

Writing an undo file may fail for these reasons:
*E828*	The file to be written cannot be created.  Perhaps you do not have
	write permissions in the directory.
"Cannot write undo file in any directory in 'undodir'"
	None of the directories in 'undodir' can be used.
"Will not overwrite with undo file, cannot read"
	A file exists with the name of the undo file to be written, but it
	cannot be read.  You may want to delete this file or rename it.
"Will not overwrite, this is not an undo file"
	A file exists with the name of the undo file to be written, but it
	does not start with the right magic number.  You may want to delete
	this file or rename it.
"Skipping undo file write, nothing to undo"
	There is no undo information to be written, nothing has been changed
	or 'undolevels' is negative.
*E829*	An error occurred while writing the undo file.  You may want to try
	again.

==============================================================================
6. Remarks about undo					*undo-remarks*

The number of changes that are remembered is set with the 'undolevels' option.
If it is zero, the Vi-compatible way is always used.  If it is negative no
undo is possible.  Use this if you are running out of memory.

*clear-undo*
When you set 'undolevels' to -1 the undo information is not immediately
cleared, this happens at the next change.  To force clearing the undo
information you can use these commands: >
	:let old_undolevels = &undolevels
	:set undolevels=-1
	:exe "normal a \<BS>\<Esc>"
	:let &undolevels = old_undolevels
	:unlet old_undolevels

Marks for the buffer ('a to 'z) are also saved and restored, together with the
text.  {Vi does this a little bit different}

When all changes have been undone, the buffer is not considered to be changed.
It is then possible to exit Vim with ":q" instead of ":q!" {not in Vi}.  Note
that this is relative to the last write of the file.  Typing "u" after ":w"
actually changes the buffer, compared to what was written, so the buffer is
considered changed then.

When manual |folding| is being used, the folds are not saved and restored.
Only changes completely within a fold will keep the fold as it was, because
the first and last line of the fold don't change.

The numbered registers can also be used for undoing deletes.  Each time you
delete text, it is put into register "1.  The contents of register "1 are
shifted to "2, etc.  The contents of register "9 are lost.  You can now get
back the most recent deleted text with the put command: '"1P'.  (also, if the
deleted text was the result of the last delete or copy operation, 'P' or 'p'
also works as this puts the contents of the unnamed register).  You can get
back the text of three deletes ago with '"3P'.

*redo-register*
If you want to get back more than one part of deleted text, you can use a
special feature of the repeat command ".".  It will increase the number of the
register used.  So if you first do ""1P", the following "." will result in a
'"2P'.  Repeating this will result in all numbered registers being inserted.

Example:	If you deleted text with 'dd....' it can be restored with
		'"1P....'.

If you don't know in which register the deleted text is, you can use the
:display command.  An alternative is to try the first register with '"1P', and
if it is not what you want do 'u.'.  This will remove the contents of the
first put, and repeat the put command for the second register.  Repeat the
'u.' until you got what you want.

vim:tw=78:ts=8:ft=help:norl:

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