# Vim documentation: undo

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    *undo.txt*      For Vim version 6.0au.  Last change: 2001 Jul 07

    		  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. 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}

    							*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.  {Vi: while not
    			moved off of it}

    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 undos 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. 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.

    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!".  {this is 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'.

    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.

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