Commit dc9bfb46 authored by Richard M. Stallman's avatar Richard M. Stallman
Browse files

(Basic Undo): Renamed from Undo. Most of text moved to new Undo node.

parent 191b577e
......@@ -21,7 +21,7 @@ use the tutorial, run Emacs and type @kbd{Control-h t}
* Moving Point:: How to move the cursor to the place where you want to
change something.
* Erasing:: Deleting and killing text.
* Undo:: Undoing recent changes in the text.
* Basic Undo:: Undoing recent changes in the text.
* Files: Basic Files. Visiting, creating, and saving files.
* Help: Basic Help. Asking what a character does.
* Blank Lines:: Commands to make or delete blank lines.
......@@ -312,73 +312,33 @@ line, it kills all the text up to the end of the line. If you type
@xref{Killing}, for more flexible ways of killing text.
@node Undo
@node Basic Undo
@section Undoing Changes
@cindex undo
@cindex changes, undoing
You can undo all the recent changes in the buffer text, up to a
certain point. Each buffer records changes individually, and the undo
command always applies to the current buffer. Usually each editing
command makes a separate entry in the undo records, but some commands
such as @code{query-replace} make many entries, and very simple commands
such as self-inserting characters are often grouped to make undoing less
tedious.
Emacs records a list of changes made in the buffer text, so you can
you can undo all the recent changes, as far as the records go.
Usually each editing command makes a separate entry in the undo
records, but sometimes an entry covers just part of a command, and
very simple commands may be grouped.
@table @kbd
@item C-x u
Undo one batch of changes---usually, one command worth (@code{undo}).
Undo one entry of the undo records---usually, one command worth
(@code{undo}).
@item C-_
@itemx C-/
The same.
@end table
@kindex C-x u
@kindex C-_
@kindex C-/
@findex undo
The command @kbd{C-x u} (or @kbd{C-_} or @kbd{C-/}) is how you undo.
The first time you give this command, it undoes the last change.
Point moves back to where it was before the command that made the
change.
Consecutive repetitions of @kbd{C-_} or @kbd{C-x u} undo earlier and
earlier changes, back to the limit of the undo information available.
If all recorded changes have already been undone, the undo command
displays an error message and does nothing.
@findex undo-only
Any command other than an undo command breaks the sequence of undo
commands. Starting from that moment, the previous undo commands become
ordinary changes that you can undo. Thus, to redo changes you have
undone, type @kbd{C-f} or any other command that will harmlessly break
the sequence of undoing, then type more undo commands. On the other
hand, if you want to ignore previous undo commands, use @kbd{M-x
undo-only}. This is like @code{undo}, but will not redo changes
you have just undone.
If you notice that a buffer has been modified accidentally, the
easiest way to recover is to type @kbd{C-_} repeatedly until the stars
disappear from the front of the mode line. At this time, all the
modifications you made have been canceled. Whenever an undo command
makes the stars disappear from the mode line, it means that the buffer
contents are the same as they were when the file was last read in or
saved.
If you do not remember whether you changed the buffer deliberately,
type @kbd{C-_} once. When you see the last change you made undone, you
will see whether it was an intentional change. If it was an accident,
leave it undone. If it was deliberate, redo the change as described
above.
Normal undo applies to the buffer as a whole. You can also
selectively undo changes in any part of the buffer (@pxref{Selective
Undo}).
Some specialized buffers do not record undo information. Buffers
whose names start with spaces never do; these buffers are used
internally by Emacs and its extensions to hold text that users don't
normally look at or edit.
Consecutive repetitions of @kbd{C-x u} (or its aliases) undo earlier
and earlier changes, back to the limit of the undo information
available. If all recorded changes have already been undone, the undo
command displays an error message and does nothing.
The undo command applies only to changes in the buffer; you can't
use it to undo mere cursor motion. However, some cursor motion
......@@ -386,42 +346,6 @@ commands set the mark, so if you use these commands from time to time,
you can move back to the neighborhoods you have moved through by
popping the mark ring (@pxref{Mark Ring}).
@vindex undo-limit
@vindex undo-strong-limit
@vindex undo-outer-limit
@cindex undo limit
When the undo information for a buffer becomes too large, Emacs
discards the oldest undo information from time to time (during garbage
collection). You can specify how much undo information to keep by
setting three variables: @code{undo-limit}, @code{undo-strong-limit},
and @code{undo-outer-limit}. Their values are expressed in units of
bytes of space.
The variable @code{undo-limit} sets a soft limit: Emacs keeps undo
data for enough commands to reach this size, and perhaps exceed it,
but does not keep data for any earlier commands beyond that. Its
default value is 20000. The variable @code{undo-strong-limit} sets a
stricter limit: a previous command (not the most recent one) which
pushes the size past this amount is itself forgotten. The default
value of @code{undo-strong-limit} is 30000.
Regardless of the values of those variables, the most recent change
is never discarded unless it gets bigger than @code{undo-outer-limit}
(normally 3,000,000). At that point, Emacs discards the undo data and
warns you about it. This is the only situation in which you cannot
undo the last command. If this happens, you can increase the value of
@code{undo-outer-limit} to make it even less likely to happen in the
future. But if you didn't expect the command to create such large
undo data, then it is probably a bug and you should report it.
@xref{Bugs,, Reporting Bugs}.
The reason the @code{undo} command has three key bindings, @kbd{C-x
u}, @kbd{C-_} and @kbd{C-/}, is that it is worthy of a
single-character key, but @kbd{C-x u} is more straightforward for
beginners to type. Meanwhile, @kbd{C--} on a text-only terminal is
really @kbd{C-_}, which makes it a natural and easily typed binding
for undoing.
@node Basic Files
@section Files
......
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