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−
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−@node Undo, Minibuffer, Basic, Top
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−@chapter Undoing Changes
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−@cindex undo
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−@cindex mistakes, correcting
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−
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−  Emacs allows you to undo all changes you make to the text of a buffer,
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−up to a certain amount of change (8000 characters).  Each buffer records
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−changes individually, and the undo command always applies to the
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−current buffer.  Usually each editing command makes a separate entry
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−in the undo records, but some commands such as @code{query-replace}
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−make many entries, and very simple commands such as self-inserting
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−characters are often grouped to make undoing less tedious.
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−
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−@table @kbd
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−@item C-x u
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−Undo one batch of changes (usually, one command's worth) (@code{undo}).
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−@item C-_
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−The same.
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−@end table
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−
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−@kindex C-x u
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−@kindex C-_
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−@findex undo
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−  The command @kbd{C-x u} or @kbd{C-_} allows you to undo changes.  The
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−first time you give this command, it undoes the last change.  Point
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−moves to the text affected by the undo, so you can see what was undone.
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−
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−  Consecutive repetitions of the @kbd{C-_} or @kbd{C-x u} commands undo
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−earlier and earlier changes, back to the limit of what has been
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−recorded.  If all recorded changes have already been undone, the undo
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−command prints an error message and does nothing.
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−
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−  Any command other than an undo command breaks the sequence of undo
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−commands.  Starting at this moment, the previous undo commands are
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−considered ordinary changes that can themselves be undone.  Thus, you can
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−redo changes you have undone by typing @kbd{C-f} or any other command
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−that have no important effect, and then using more undo commands.
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−
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−  If you notice that a buffer has been modified accidentally, the
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−easiest way to recover is to type @kbd{C-_} repeatedly until the stars
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−disappear from the front of the mode line.  When that happens, all the
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−modifications you made have been canceled.  If you do not remember
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−whether you changed the buffer deliberately, type @kbd{C-_} once. When
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−you see Emacs undo the last change you made, you probably remember why you
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−made it.  If the change was an accident, leave it undone.  If it was
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−deliberate, redo the change as described in the preceding paragraph.
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−
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−  Whenever an undo command makes the stars disappear from the mode line,
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−the buffer contents is the same as it was when the file was last read in
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−or saved.
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−
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−  Not all buffers record undo information.  Buffers whose names start with
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−spaces don't; these buffers are used internally by Emacs and its extensions
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−to hold text that users don't normally look at or edit.  Minibuffers,
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−help buffers, and documentation buffers also don't record undo information.
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−
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−  Emacs can remember at most 8000 or so characters of deleted or
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−modified text in any one buffer for reinsertion by the undo command.
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−There is also a limit on the number of individual insert, delete, or
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−change actions that Emacs can remember.
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−
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−  There are two keys to run the @code{undo} command, @kbd{C-x u} and
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−@kbd{C-_}, because on some keyboards, it is not obvious how to type
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−@kbd{C-_}. @kbd{C-x u} is an alternative you can type in the same
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−fashion on any terminal.