@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2001, 2002,
@c   2003, 2004, 2005, 2006, 2007, 2008  Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Fixit, Keyboard Macros, Search, Top
@chapter Commands for Fixing Typos
@cindex typos, fixing
@cindex mistakes, correcting

  In this chapter we describe the commands that are especially useful for
the times when you catch a mistake in your text just after you have made
it, or change your mind while composing text on the fly.

  The most fundamental command for correcting erroneous editing is the
undo command, @kbd{C-x u} or @kbd{C-_} or @kbd{C-/}.  This command
undoes a single command (usually), a part of a command (in the case of
@code{query-replace}), or several consecutive self-inserting
characters.  Consecutive repetitions of the undo command undo earlier
and earlier changes, back to the limit of the undo information
available.  @xref{Undo}, for more information.

@menu
* Undo::        The Undo commands.
* Kill Errors:: Commands to kill a batch of recently entered text.
* Transpose::   Exchanging two characters, words, lines, lists...
* Fixing Case:: Correcting case of last word entered.
* Spelling::    Apply spelling checker to a word, or a whole file.
@end menu

@node Undo
@section Undo
@cindex undo
@cindex changes, undoing

  The @dfn{undo} commands undo recent changes in the buffer's text.
Each buffer records changes individually, and the undo command always
applies to the current buffer.  You can undo all the changes in a
buffer for as far as back these records go.  Usually each editing
command makes a separate entry in the undo records, but some commands
such as @code{query-replace} divide their changes into multiple
entries for flexibility in undoing.  Meanwhile, self-inserting
characters are usually grouped to make undoing less tedious.

@table @kbd
@item C-x u
@itemx C-_
@itemx C-/
Undo one entry in the current buffer's undo records (@code{undo}).
@end table

@kindex C-x u
@kindex C-_
@kindex C-/
@findex undo
  To begin to undo, type the command @kbd{C-/} (or its aliases,
@kbd{C-_} or @kbd{C-x u}).  This undoes the most recent change in the
buffer, and moves point back to where it was before that change.

  Consecutive repetitions of @kbd{C-/} (or its aliases) undo earlier
and earlier changes in the current buffer, back to the limit of the
current buffer's undo records.  If all the recorded changes have
already been undone, the undo command just signals an error.

  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
below.

@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 undo commands again.  On the
other hand, if you want to resume undoing, without redoing previous
undo commands, use @kbd{M-x undo-only}.  This is like @code{undo}, but
will not redo changes you have just undone.

@cindex selective undo
@kindex C-u C-/
  When there is an active region, any use of @code{undo} performs
@dfn{selective undo}, undoing the most recent change within the
region, instead of the entire buffer.  However, when Transient Mark
mode is off (@pxref{Persistent Mark}), @kbd{C-/} always operates on
the entire buffer, ignoring the region.  In this case, you can perform
selective undo by supplying a prefix argument to the @code{undo}
command: @kbd{C-u C-/} or @kbd{C-u C-x u}.  To undo further changes in
the same region, repeat the @code{undo} command (no prefix argument is
needed).

  Some specialized buffers do not make undo records.  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.

@vindex undo-limit
@vindex undo-strong-limit
@vindex undo-outer-limit
@cindex undo limit
  When the undo records for a buffer becomes too large, Emacs
discards the oldest undo records from time to time (during garbage
collection).  You can specify how much undo records 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 remember and 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 Kill Errors
@section Killing Your Mistakes

@table @kbd
@item @key{DEL}
Delete last character (@code{delete-backward-char}).
@item M-@key{DEL}
Kill last word (@code{backward-kill-word}).
@item C-x @key{DEL}
Kill to beginning of sentence (@code{backward-kill-sentence}).
@end table

  The @key{DEL} character (@code{delete-backward-char}) is the most
important correction command.  It deletes the character before point.
When @key{DEL} follows a self-inserting character command, you can think
of it as canceling that command.  However, avoid the confusion of thinking
of @key{DEL} as a general way to cancel a command!

  When your mistake is longer than a couple of characters, it might be
more convenient to use @kbd{M-@key{DEL}} or @kbd{C-x @key{DEL}}.
@kbd{M-@key{DEL}} kills back to the start of the last word, and @kbd{C-x
@key{DEL}} kills back to the start of the last sentence.  @kbd{C-x
@key{DEL}} is particularly useful when you change your mind about the
phrasing of the text you are writing.  @kbd{M-@key{DEL}} and @kbd{C-x
@key{DEL}} save the killed text for @kbd{C-y} and @kbd{M-y} to
retrieve.  @xref{Yanking}.@refill

  @kbd{M-@key{DEL}} is often useful even when you have typed only a few
characters wrong, if you know you are confused in your typing and aren't
sure exactly what you typed.  At such a time, you cannot correct with
@key{DEL} except by looking at the screen to see what you did.  Often it
requires less thought to kill the whole word and start again.

@node Transpose
@section Transposing Text

@table @kbd
@item C-t
Transpose two characters (@code{transpose-chars}).
@item M-t
Transpose two words (@code{transpose-words}).
@item C-M-t
Transpose two balanced expressions (@code{transpose-sexps}).
@item C-x C-t
Transpose two lines (@code{transpose-lines}).
@end table

@kindex C-t
@findex transpose-chars
  The common error of transposing two characters can be fixed, when they
are adjacent, with the @kbd{C-t} command (@code{transpose-chars}).  Normally,
@kbd{C-t} transposes the two characters on either side of point.  When
given at the end of a line, rather than transposing the last character of
the line with the newline, which would be useless, @kbd{C-t} transposes the
last two characters on the line.  So, if you catch your transposition error
right away, you can fix it with just a @kbd{C-t}.  If you don't catch it so
fast, you must move the cursor back between the two transposed
characters before you type @kbd{C-t}.  If you transposed a space with
the last character of the word before it, the word motion commands are
a good way of getting there.  Otherwise, a reverse search (@kbd{C-r})
is often the best way.  @xref{Search}.

@kindex C-x C-t
@findex transpose-lines
@kindex M-t
@findex transpose-words
@c Don't index C-M-t and transpose-sexps here, they are indexed in
@c programs.texi, in the "List Commands" node.
@c @kindex C-M-t
@c @findex transpose-sexps
  @kbd{M-t} transposes the word before point with the word after point
(@code{transpose-words}).  It moves point forward over a word,
dragging the word preceding or containing point forward as well.  The
punctuation characters between the words do not move.  For example,
@w{@samp{FOO, BAR}} transposes into @w{@samp{BAR, FOO}} rather than
@samp{@w{BAR FOO,}}.

  @kbd{C-M-t} (@code{transpose-sexps}) is a similar command for
transposing two expressions (@pxref{Expressions}), and @kbd{C-x C-t}
(@code{transpose-lines}) exchanges lines.  They work like @kbd{M-t}
except as regards what units of text they transpose.

  A numeric argument to a transpose command serves as a repeat count: it
tells the transpose command to move the character (word, expression, line)
before or containing point across several other characters (words,
expressions, lines).  For example, @kbd{C-u 3 C-t} moves the character before
point forward across three other characters.  It would change
@samp{f@point{}oobar} into @samp{oobf@point{}ar}.  This is equivalent to
repeating @kbd{C-t} three times.  @kbd{C-u - 4 M-t} moves the word
before point backward across four words.  @kbd{C-u - C-M-t} would cancel
the effect of plain @kbd{C-M-t}.@refill

  A numeric argument of zero is assigned a special meaning (because
otherwise a command with a repeat count of zero would do nothing): to
transpose the character (word, expression, line) ending after point
with the one ending after the mark.

@node Fixing Case
@section Case Conversion

@table @kbd
@item M-- M-l
Convert last word to lower case.  Note @kbd{Meta--} is Meta-minus.
@item M-- M-u
Convert last word to all upper case.
@item M-- M-c
Convert last word to lower case with capital initial.
@end table

@kindex M-@t{-} M-l
@kindex M-@t{-} M-u
@kindex M-@t{-} M-c
  A very common error is to type words in the wrong case.  Because of this,
the word case-conversion commands @kbd{M-l}, @kbd{M-u} and @kbd{M-c} have a
special feature when used with a negative argument: they do not move the
cursor.  As soon as you see you have mistyped the last word, you can simply
case-convert it and go on typing.  @xref{Case}.@refill

@node Spelling
@section Checking and Correcting Spelling
@cindex spelling, checking and correcting
@cindex checking spelling
@cindex correcting spelling

  This section describes the commands to check the spelling of a single
word or of a portion of a buffer.  These commands work with the spelling
checker programs Aspell and Ispell, which are not part of Emacs.
@ifnottex
@xref{Top, Aspell,, aspell, The Aspell Manual}.
@end ifnottex

@table @kbd
@item M-x flyspell-mode
Enable Flyspell mode, which highlights all misspelled words.
@item M-x flyspell-prog-mode
Enable Flyspell mode for comments and strings only.
@item M-$
Check and correct spelling of the word at point (@code{ispell-word}).
@item M-@key{TAB}
@itemx @key{ESC} @key{TAB}
Complete the word before point based on the spelling dictionary
(@code{ispell-complete-word}).
@item M-x ispell
Spell-check the active region or the current buffer.
@item M-x ispell-buffer
Check and correct spelling of each word in the buffer.
@item M-x ispell-region
Check and correct spelling of each word in the region.
@item M-x ispell-message
Check and correct spelling of each word in a draft mail message,
excluding cited material.
@item M-x ispell-change-dictionary @key{RET} @var{dict} @key{RET}
Restart the Aspell or Ispell process, using @var{dict} as the dictionary.
@item M-x ispell-kill-ispell
Kill the Aspell or Ispell subprocess.
@end table

@cindex Flyspell mode
@findex flyspell-mode
  Flyspell mode is a fully-automatic way to check spelling as you edit
in Emacs.  It operates by checking words as you change or insert them.
When it finds a word that it does not recognize, it highlights that
word.  This does not interfere with your editing, but when you see the
highlighted word, you can move to it and fix it.  Type @kbd{M-x
flyspell-mode} to enable or disable this mode in the current buffer.

  When Flyspell mode highlights a word as misspelled, you can click on
it with @kbd{Mouse-2} to display a menu of possible corrections and
actions.  You can also correct the word by editing it manually in any
way you like.

@findex flyspell-prog-mode
Flyspell Prog mode works just like ordinary Flyspell mode, except that
it only checks words in comments and string constants.  This feature
is useful for editing programs.  Type @kbd{M-x flyspell-prog-mode} to
enable or disable this mode in the current buffer.

  The other Emacs spell-checking features check or look up words when
you give an explicit command to do so.

@kindex M-$
@findex ispell-word
  To check the spelling of the word around or before point, and
optionally correct it as well, use the command @kbd{M-$}
(@code{ispell-word}).  If the word is not correct, Emacs offers you
various alternatives for what to do about it.  If a region is active,
@kbd{M-$} checks the spelling of all words within the region
(@pxref{Mark}).  (However, when Transient Mark mode is off, @kbd{M-$}
always acts on the word around or before point, ignoring the region.
@xref{Persistent Mark}.)

@findex ispell
@cindex spell-checking the active region
  The @kbd{M-x ispell} command performs spell-checking on the entire
buffer if no region is active, or on region if one is active.  (When
Transient Mark mode is off, it always acts on the entire buffer,
ignoring the region.)

@findex ispell-buffer
@findex ispell-region
  The commands @kbd{M-x ispell-buffer} and @kbd{M-x ispell-region}
explicitly perform spell-checking on the entire buffer or the region
respectively.

  To check spelling in an email message you are writing, use @kbd{M-x
ispell-message}; that command checks the whole buffer, except for
material that is indented or appears to be cited from other messages.

  Each time these commands encounter an incorrect word, they ask you
what to do.  They display a list of alternatives, usually including
several ``near-misses''---words that are close to the word being
checked.  Then you must type a single-character response.  Here are
the valid responses:

@table @kbd
@item @key{SPC}
Skip this word---continue to consider it incorrect, but don't change it
here.

@item r @var{new} @key{RET}
Replace the word (just this time) with @var{new}.  (The replacement
string will be rescanned for more spelling errors.)

@item R @var{new} @key{RET}
Replace the word with @var{new}, and do a @code{query-replace} so you
can replace it elsewhere in the buffer if you wish.  (The replacements
will be rescanned for more spelling errors.)

@item @var{digit}
Replace the word (just this time) with one of the displayed
near-misses.  Each near-miss is listed with a digit; type that digit to
select it.

@item a
Accept the incorrect word---treat it as correct, but only in this
editing session.

@item A
Accept the incorrect word---treat it as correct, but only in this
editing session and for this buffer.

@item i
Insert this word in your private dictionary file so that Aspell or Ispell will
consider it correct from now on, even in future sessions.

@item u
Insert the lower-case version of this word in your private dic@-tion@-ary
file.

@item m
Like @kbd{i}, but you can also specify dictionary completion
information.

@item l @var{word} @key{RET}
Look in the dictionary for words that match @var{word}.  These words
become the new list of ``near-misses''; you can select one of them as
the replacement by typing a digit.  You can use @samp{*} in @var{word} as a
wildcard.

@item C-g
Quit interactive spell checking, leaving point at the word that was
being checked.  You can restart checking again afterward with @kbd{C-u
M-$}.

@item X
Same as @kbd{C-g}.

@item x
Quit interactive spell checking and move point back to where it was
when you started spell checking.

@item q
Quit interactive spell checking and kill the Ispell subprocess.

@item C-l
Refresh the screen.

@item C-z
This key has its normal command meaning (suspend Emacs or iconify this
frame).

@item ?
Show the list of options.
@end table

@findex ispell-complete-word
  The command @code{ispell-complete-word}, which is bound to the key
@kbd{M-@key{TAB}} in Text mode and related modes, shows a list of
completions based on spelling correction.  Insert the beginning of a
word, and then type @kbd{M-@key{TAB}}; the command displays a
completion list window.  (If your window manager intercepts
@kbd{M-@key{TAB}}, type @kbd{@key{ESC} @key{TAB}} or @kbd{C-M-i}.)  To
choose one of the completions listed, click @kbd{Mouse-2} or
@kbd{Mouse-1} fast on it, or move the cursor there in the completions
window and type @key{RET}.  @xref{Text Mode}.

@ignore
@findex reload-ispell
  The first time you use any of the spell checking commands, it starts
an Ispell subprocess.  The first thing the subprocess does is read your
private dictionary, which defaults to the file @file{~/ispell.words}.
Words that you ``insert'' with the @kbd{i} command are added to that
file, but not right away---only at the end of the interactive
replacement procedure.  Use the @kbd{M-x reload-ispell} command to
reload your private dictionary if you edit the file outside of Ispell.
@end ignore

@cindex @code{ispell} program
@findex ispell-kill-ispell
  Once started, the Aspell or Ispell subprocess continues to run
(waiting for something to do), so that subsequent spell checking
commands complete more quickly.  If you want to get rid of the
process, use @kbd{M-x ispell-kill-ispell}.  This is not usually
necessary, since the process uses no time except when you do spelling
correction.

@vindex ispell-dictionary
  Ispell and Aspell use two dictionaries together for spell checking: the
standard dictionary and your private dictionary.  The variable
@code{ispell-dictionary} specifies the file name to use for the
standard dictionary; a value of @code{nil} selects the default
dictionary.  The command @kbd{M-x ispell-change-dictionary} sets this
variable and then restarts the subprocess, so that it will use
a different standard dictionary.

@vindex ispell-complete-word-dict
  Aspell and Ispell use a separate dictionary for word completion.
The variable @code{ispell-complete-word-dict} specifies the file name
of this dictionary.  The completion dictionary must be different
because it cannot use root and affix information.  For some languages
there is a spell checking dictionary but no word completion
dictionary.

@ignore
   arch-tag: 3359a443-96ed-448f-9f05-c8111ba8eac0
@end ignore
