Merge changes from emacs-23 branch

[bpt/emacs.git] / doc / emacs / basic.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2011
@c   Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Basic, Minibuffer, Exiting, Top
@chapter Basic Editing Commands

@kindex C-h t
@findex help-with-tutorial
  Here we explain the basics of how to enter text, make corrections,
and save the text in a file.  If this material is new to you, we
suggest you first run the Emacs learn-by-doing tutorial, by typing
@kbd{Control-h t} inside Emacs.  (@code{help-with-tutorial}).

@menu

* Inserting Text::      Inserting text by simply typing it.
* Moving Point::        Moving the cursor to the place where you want to
                          change something.
* Erasing::             Deleting and killing 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::         Making and deleting blank lines.
* Continuation Lines::  How Emacs displays lines too wide for the screen.
* Position Info::       What page, line, row, or column is point on?
* Arguments::           Numeric arguments for repeating a command N times.
* Repeating::           Repeating the previous command quickly.
@end menu

@node Inserting Text
@section Inserting Text

@cindex insertion
@cindex graphic characters
  You can insert an ordinary @dfn{graphic character} (e.g., @samp{a},
@samp{B}, @samp{3}, and @samp{=}) by typing the associated key.  This
adds the character to the buffer at point.  Insertion moves point
forward, so that point remains just after the inserted text.
@xref{Point}.

@kindex RET
@cindex newline
  To end a line and start a new one, type @key{RET}.  This key may be
labeled @key{Return} or @key{Enter} on your keyboard, but we refer to
it as @key{RET} in this manual.  Pressing it inserts a newline
character in the buffer.  If point is at the end of the line, this
creates a new blank line after it; if point is in the middle of a
line, the line is split at that position.

  As we explain later in this manual, you can change the way Emacs
handles text insertion by turning on @dfn{minor modes}.  For instance,
if you turn on a minor mode called @dfn{Auto Fill} mode, Emacs can
split lines automatically when they become too long (@pxref{Filling}).
If you turn on a minor mode called @dfn{Overwrite} mode, inserted
characters replace (overwrite) existing text, instead of shoving it to
the right.  @xref{Minor Modes}.

@cindex quoting
@kindex C-q
@findex quoted-insert
  Only graphic characters can be inserted by typing the associated
key; other keys act as editing commands and do not insert themselves.
For instance, @kbd{DEL} runs the command @code{delete-backward-char}
by default (some modes bind it to a different command); it does not
insert a literal @samp{DEL} character (@acronym{ASCII} character code
127).

  To insert a non-graphic character, or a character that your keyboard
does not support, first @dfn{quote} it by typing @kbd{C-q}
(@code{quoted-insert}).  There are two ways to use @kbd{C-q}:

@itemize @bullet
@item
@kbd{C-q} followed by any non-graphic character (even @kbd{C-g})
inserts that character.  For instance, @kbd{C-q @key{DEL}} inserts a
literal @samp{DEL} character.

@item
@kbd{C-q} followed by a sequence of octal digits inserts the character
with the specified octal character code.  You can use any number of
octal digits; any non-digit terminates the sequence.  If the
terminating character is @key{RET}, it serves only to terminate the
sequence.  Any other non-digit terminates the sequence and then acts
as normal input---thus, @kbd{C-q 1 0 1 B} inserts @samp{AB}.

The use of octal sequences is disabled in ordinary non-binary
Overwrite mode, to give you a convenient way to insert a digit instead
of overwriting with it.
@end itemize

@vindex read-quoted-char-radix
@noindent
To use decimal or hexadecimal instead of octal, set the variable
@code{read-quoted-char-radix} to 10 or 16.  If the radix is 16,
the letters @kbd{a} to @kbd{f} serve as part of a character code,
just like digits.  Case is ignored.

  A numeric argument tells @kbd{C-q} how many copies of the quoted
character to insert (@pxref{Arguments}).

@findex ucs-insert
@kindex C-x 8 RET
@cindex Unicode characters, inserting
@cindex insert Unicode character
@cindex characters, inserting by name or code-point
  Instead of @kbd{C-q}, you can use @kbd{C-x 8 @key{RET}}
(@code{ucs-insert}) to insert a character based on its Unicode name or
code-point.  This command prompts for a character to insert, using
the minibuffer; you can specify the character using either (i) the
character's name in the Unicode standard, or (ii) the character's
code-point in the Unicode standard.  If you specify the character's
name, the command provides completion.

@node Moving Point
@section Changing the Location of Point

@cindex arrow keys
@cindex moving point
@cindex movement
@cindex cursor motion
@cindex moving the cursor
  To do more than insert characters, you have to know how to move
point (@pxref{Point}).  The keyboard commands @kbd{C-f}, @kbd{C-b},
@kbd{C-n}, and @kbd{C-p} move point to the right, left, up and down
respectively.  These are equivalent to the commands @kbd{@key{right}},
@kbd{@key{left}}, @kbd{@key{down}}, and @kbd{@key{up}}, entered using
the @dfn{arrow keys} present on many keyboards.  Many Emacs users find
that it is slower to use the arrow keys than the equivalent control
keys.  You can also click the left mouse button to move point to the
position clicked.  Emacs also provides a variety of additional
keyboard commands that move point in more sophisticated ways.

@kindex C-a
@kindex C-e
@kindex C-f
@kindex C-b
@kindex C-n
@kindex C-p
@kindex M->
@kindex M-<
@kindex M-r
@kindex LEFT
@kindex RIGHT
@kindex UP
@kindex DOWN
@findex move-beginning-of-line
@findex move-end-of-line
@findex forward-char
@findex backward-char
@findex right-char
@findex left-char
@findex next-line
@findex previous-line
@findex beginning-of-buffer
@findex end-of-buffer
@findex goto-char
@findex goto-line
@findex move-to-window-line
@table @kbd
@item C-a
@itemx @key{Home}
Move to the beginning of the line (@code{move-beginning-of-line}).
@item C-e
@itemx @key{End}
Move to the end of the line (@code{move-end-of-line}).
@item C-f
Move forward one character (@code{forward-char}).
@item @key{right}
Move one character to the right (@code{right-char}).  This
moves one character forward in text that is read in the usual
left-to-right direction, but one character @emph{backward} if the text
is read right-to-left, as needed for right-to-left scripts such as
Arabic.  @xref{Bidirectional Editing}.
@item C-b
Move backward one character (@code{backward-char}).
@item @key{left}
Move one character to the left (@code{left-char}).  This
moves one character backward in left-to-right text and one character
forward in right-to-left text.
@item M-f
@itemx M-@key{right}
Move forward one word (@code{forward-word}).
@item C-@key{right}
Move one word to the right (@code{right-word}).  This moves one word
forward in left-to-right text and one word backward in right-to-left
text.
@item M-b
@itemx M-@key{left}
Move backward one word (@code{backward-word}).
@item C-@key{left}
Move one word to the left (@code{left-word}).  This moves one word
backward in left-to-right text and one word forward in right-to-left
text.
@item C-n
@itemx @key{down}
Move down one screen line (@code{next-line}).  This command attempts
to keep the horizontal position unchanged, so if you start in the
middle of one line, you move to the middle of the next.
@item C-p
@itemx @key{up}
Move up one screen line (@code{previous-line}).  This command
preserves position within the line, like @kbd{C-n}.
@item M-r
Without moving the text on the screen, reposition point on the left
margin of the center-most text line of the window; on subsequent
consecutive invocations, move point to the left margin of the top-most
line, the bottom-most line, and so forth, in cyclic order
(@code{move-to-window-line-top-bottom}).

A numeric argument says which screen line to place point on, counting
downward from the top of the window (zero means the top line).  A
negative argument counts lines up from the bottom (@minus{}1 means the
bottom line).

@item M-<
Move to the top of the buffer (@code{beginning-of-buffer}).  With
numeric argument @var{n}, move to @var{n}/10 of the way from the top.
@xref{Arguments}, for more information on numeric arguments.@refill
@item M->
Move to the end of the buffer (@code{end-of-buffer}).
@item C-v
@itemx @key{PageDown}
@itemx @key{next}
Scroll the display one screen forward, and move point if necessary to
put it on the screen (@code{scroll-up}).  If your keyboard has a
@key{PageDown} key (sometimes labelled @key{next}), it does the same
thing as @key{C-v}.  Scrolling commands are described further in
@ref{Scrolling}.
@item M-v
@itemx @key{PageUp}
@itemx @key{prior}
Scroll one screen backward, and move point if necessary to put it on
the screen (@code{scroll-down}).  If your keyboard has a @key{PageUp}
key (sometimes labelled @key{prior}), it does the same thing as
@kbd{M-v}.
@item M-x goto-char
Read a number @var{n} and move point to buffer position @var{n}.
Position 1 is the beginning of the buffer.
@item M-g M-g
@itemx M-g g
Read a number @var{n} and move point to the beginning of line number
@var{n} (@code{goto-line}).  Line 1 is the beginning of the buffer.  If
point is on or just after a number in the buffer, that is the default
for @var{n}.  Just type @key{RET} in the minibuffer to use it.  You can
also specify @var{n} by giving @kbd{M-g M-g} a numeric prefix argument.
@xref{Select Buffer}, for the behavior of @kbd{M-g M-g} when you give it
a plain prefix argument.
@item C-x C-n
@findex set-goal-column
@kindex C-x C-n
Use the current column of point as the @dfn{semipermanent goal column}
for @kbd{C-n} and @kbd{C-p} (@code{set-goal-column}).  When a
semipermanent goal column is in effect, those commands always try to
move to this column, or as close as possible to it, after moving
vertically.  The goal column remains in effect until canceled.
@item C-u C-x C-n
Cancel the goal column.  Henceforth, @kbd{C-n} and @kbd{C-p} try to
preserve the horizontal position, as usual.
@end table

@vindex line-move-visual
  When a line of text in the buffer is longer than the width of the
window, Emacs usually displays it on two or more @dfn{screen lines}.
For convenience, @kbd{C-n} and @kbd{C-p} move point by screen lines,
as do the equivalent keys @kbd{@key{down}} and @kbd{@key{up}}.  You
can force these commands to move according to @dfn{logical lines}
(i.e., according to the text lines in the buffer) by setting the
variable @code{line-move-visual} to @code{nil}; if a logical line
occupies multiple screen lines, the cursor then skips over the
additional screen lines.  Moving by logical lines was the default
behavior prior to Emacs 23.1.  For details, see @ref{Continuation
Lines}.  @xref{Variables}, for how to set variables such as
@code{line-move-visual}.

  Unlike @kbd{C-n} and @kbd{C-p}, most of the Emacs commands that work
on lines work on @emph{logical} lines.  For instance, @kbd{C-a}
(@code{move-beginning-of-line}) and @kbd{C-e}
(@code{move-end-of-line}) respectively move to the beginning and end
of the logical line.  Whenever we encounter commands that work on
screen lines, such as @kbd{C-n} and @kbd{C-p}, we will point these
out.

@vindex track-eol
  When @code{line-move-visual} is @code{nil}, you can also set the
variable @code{track-eol} to a non-@code{nil} value.  Then @kbd{C-n}
and @kbd{C-p}, when starting at the end of the logical line, move to
the end of the next logical line.  Normally, @code{track-eol} is
@code{nil}.

@vindex next-line-add-newlines
  @kbd{C-n} normally stops at the end of the buffer when you use it on
the last line of the buffer.  However, if you set the variable
@code{next-line-add-newlines} to a non-@code{nil} value, @kbd{C-n} on
the last line of a buffer creates an additional line at the end and
moves down into it.

@node Erasing
@section Erasing Text

@table @kbd
@item @key{DEL}
@itemx @key{Backspace}
Delete the character before point (@code{delete-backward-char}).
@item C-d
@itemx @key{Delete}
Delete the character after point (@code{delete-char}).
@item C-k
Kill to the end of the line (@code{kill-line}).
@item M-d
Kill forward to the end of the next word (@code{kill-word}).
@item M-@key{DEL}
Kill back to the beginning of the previous word
(@code{backward-kill-word}).
@end table

   The key @kbd{@key{DEL}} (@code{delete-backward-char}) removes the
character before point, moving the cursor and all the characters after
it backwards.  On most keyboards, @key{DEL} is labelled
@key{Backspace}, but we refer to it as @key{DEL} in this manual.  Do
not confuse @key{DEL} with another key, labelled @key{Delete}, that
exists on many keyboards; we will discuss @key{Delete} momentarily.

  Typing @key{DEL} when the cursor is at the beginning of a line
deletes the preceding newline character, joining the line with the one
before it.

  On some text-only terminals, Emacs may not recognize the @key{DEL}
key properly.  If @key{DEL} does not do the right thing (e.g., if it
deletes characters forwards), see @ref{DEL Does Not Delete}.

@cindex killing characters and lines
@cindex deleting characters and lines
@cindex erasing characters and lines
  The key @kbd{C-d} (@code{delete-char}) deletes the character after
point, i.e., the character under the cursor.  This shifts the rest of
the text on the line to the left.  If you type @kbd{C-d} at the end of
a line, it joins that line with the following line.  This command is
also bound to the key labelled @key{Delete} on many keyboards.

  To erase a larger amount of text, use the @kbd{C-k} key, which
erases (kills) a line at a time.  If you type @kbd{C-k} at the
beginning or middle of a line, it kills all the text up to the end of
the line.  If you type @kbd{C-k} at the end of a line, it joins that
line with the following line.

  To learn more about killing text, see @ref{Killing}.

@node Basic Undo
@section Undoing Changes

@table @kbd
@item C-/
Undo one entry of the undo records---usually, one command worth
(@code{undo}).
@itemx C-x u
@item C-_
The same.
@end table

  Emacs records a list of changes made in the buffer text, so you can
undo recent changes.  This is done using the @code{undo} command,
which is bound to @kbd{C-/} (as well as @kbd{C-x u} and @kbd{C-_}).
Normally, this command undoes the last change, moving point back to
where it was before the change.  The undo command applies only to
changes in the buffer; you can't use it to undo cursor motion.

  Although each editing command usually makes a separate entry in the
undo records, very simple commands may be grouped together.
Sometimes, an entry may cover just part of a complex command.

  If you repeat @kbd{C-/} (or its aliases), each repetition undoes
another, earlier change, 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.

  To learn more about the @code{undo} command, see @ref{Undo}.

@node Basic Files
@section Files

  Text that you insert in an Emacs buffer lasts only as long as the
Emacs session.  To keep any text permanently, you must put it in a
@dfn{file}.  Files are named units of text which are stored by the
operating system for you to retrieve later by name.  To use the
contents of a file in any way, including editing it with Emacs, you
must specify the file name.

  Suppose there is a file named @file{test.emacs} in your home
directory.  To begin editing this file in Emacs, type

@example
C-x C-f test.emacs @key{RET}
@end example

@noindent
Here the file name is given as an @dfn{argument} to the command @kbd{C-x
C-f} (@code{find-file}).  That command uses the @dfn{minibuffer} to
read the argument, and you type @key{RET} to terminate the argument
(@pxref{Minibuffer}).

  Emacs obeys this command by @dfn{visiting} the file: it creates a
buffer, copies the contents of the file into the buffer, and then
displays the buffer for editing.  If you alter the text, you can
@dfn{save} the new text in the file by typing @kbd{C-x C-s}
(@code{save-buffer}).  This copies the altered buffer contents back
into the file @file{test.emacs}, making them permanent.  Until you
save, the changed text exists only inside Emacs, and the file
@file{test.emacs} is unaltered.

  To create a file, just visit it with @kbd{C-x C-f} as if it already
existed.  This creates an empty buffer, in which you can insert the
text you want to put in the file.  Emacs actually creates the file the
first time you save this buffer with @kbd{C-x C-s}.

  To learn more about using files in Emacs, see @ref{Files}.

@node Basic Help
@section Help

@cindex getting help with keys
  If you forget what a key does, you can find out with the Help
character, which is @kbd{C-h} (or @key{F1}, which is an alias for
@kbd{C-h}).  Type @kbd{C-h k}, followed by the key of interest; for
example, @kbd{C-h k C-n} tells you what @kbd{C-n} does.  @kbd{C-h} is
a prefix key; @kbd{C-h k} is just one of its subcommands (the command
@code{describe-key}).  The other subcommands of @kbd{C-h} provide
different kinds of help.  Type @kbd{C-h} twice to get a description of
all the help facilities.  @xref{Help}.

@node Blank Lines
@section Blank Lines

@cindex inserting blank lines
@cindex deleting blank lines
  Here are special commands and techniques for inserting and deleting
blank lines.

@table @kbd
@item C-o
Insert a blank line after the cursor (@code{open-line}).
@item C-x C-o
Delete all but one of many consecutive blank lines
(@code{delete-blank-lines}).
@end table

@kindex C-o
@kindex C-x C-o
@cindex blank lines
@findex open-line
@findex delete-blank-lines
  We have seen how @kbd{@key{RET}} (@code{newline}) starts a new line
of text.  However, it may be easier to see what you are doing if you
first make a blank line and then insert the desired text into it.
This is easy to do using the key @kbd{C-o} (@code{open-line}), which
inserts a newline after point but leaves point in front of the
newline.  After @kbd{C-o}, type the text for the new line.

  You can make several blank lines by typing @kbd{C-o} several times, or
by giving it a numeric argument specifying how many blank lines to make.
@xref{Arguments}, for how.  If you have a fill prefix, the @kbd{C-o}
command inserts the fill prefix on the new line, if typed at the
beginning of a line.  @xref{Fill Prefix}.

  The easy way to get rid of extra blank lines is with the command
@kbd{C-x C-o} (@code{delete-blank-lines}).  If point lies within a run
of several blank lines, @kbd{C-x C-o} deletes all but one of them.  If
point is on a single blank line, @kbd{C-x C-o} deletes it.  If point
is on a nonblank line, @kbd{C-x C-o} deletes all following blank
lines, if any exists.

@node Continuation Lines
@section Continuation Lines

@cindex continuation line
@cindex wrapping
@cindex line wrapping
@cindex fringes, and continuation lines
  Sometimes, a line of text in the buffer---a @dfn{logical line}---is
too long to fit in the window, and Emacs displays it as two or more
@dfn{screen lines}.  This is called @dfn{line wrapping} or
@dfn{continuation}, and the long logical line is called a
@dfn{continued line}.  On a graphical display, Emacs indicates line
wrapping with small bent arrows in the left and right window fringes.
On a text-only terminal, Emacs indicates line wrapping by displaying a
@samp{\} character at the right margin.

  Most commands that act on lines act on logical lines, not screen
lines.  For instance, @kbd{C-k} kills a logical line.  As described
earlier, @kbd{C-n} (@code{next-line}) and @kbd{C-p}
(@code{previous-line}) are special exceptions: they move point down
and up, respectively, by one screen line (@pxref{Moving Point}).

@cindex truncation
@cindex line truncation, and fringes
  Emacs can optionally @dfn{truncate} long logical lines instead of
continuing them.  This means that every logical line occupies a single
screen line; if it is longer than the width of the window, the rest of
the line is not displayed.  On a graphical display, a truncated line
is indicated by a small straight arrow in the right fringe; on a
text-only terminal, it is indicated by a @samp{$} character in the
right margin.  @xref{Line Truncation}.

  By default, continued lines are wrapped at the right window edge.
Since the wrapping may occur in the middle of a word, continued lines
can be difficult to read.  The usual solution is to break your lines
before they get too long, by inserting newlines.  If you prefer, you
can make Emacs insert a newline automatically when a line gets too
long, by using Auto Fill mode.  @xref{Filling}.

@cindex word wrap
  Sometimes, you may need to edit files containing many long logical
lines, and it may not be practical to break them all up by adding
newlines.  In that case, you can use Visual Line mode, which enables
@dfn{word wrapping}: instead of wrapping long lines exactly at the
right window edge, Emacs wraps them at the word boundaries (i.e.,
space or tab characters) nearest to the right window edge.  Visual
Line mode also redefines editing commands such as @code{C-a},
@code{C-n}, and @code{C-k} to operate on screen lines rather than
logical lines.  @xref{Visual Line Mode}.

@node Position Info
@section Cursor Position Information

  Here are commands to get information about the size and position of
parts of the buffer, and to count lines.

@table @kbd
@item M-x what-page
Display the page number of point, and the line number within that page.
@item M-x what-line
Display the line number of point in the whole buffer.
@item M-x line-number-mode
@itemx M-x column-number-mode
Toggle automatic display of the current line number or column number.
@xref{Optional Mode Line}.
@item M-x count-lines-region
Display the number of lines in the current region.  Normally bound to
@kbd{M-=}, except in a few specialist modes.  @xref{Mark}, for
information about the region.
@item M-x count-words-region
Display the number of words in the current region.
@item C-x =
Display the character code of character after point, character position of
point, and column of point (@code{what-cursor-position}).
@item M-x hl-line-mode
Enable or disable highlighting of the current line.  @xref{Cursor
Display}.
@item M-x size-indication-mode
Toggle automatic display of the size of the buffer.
@xref{Optional Mode Line}.
@end table

@findex what-page
@findex what-line
@cindex line number commands
@cindex location of point
@cindex cursor location
@cindex point location
  @kbd{M-x what-line} displays the current line number in the echo
area.  This command is usually redundant, because the current line
number is shown in the mode line (@pxref{Mode Line}).  However, if you
narrow the buffer, the mode line shows the line number relative to
the accessible portion (@pxref{Narrowing}).  By contrast,
@code{what-line} displays both the line number relative to the
narrowed region and the line number relative to the whole buffer.

  @kbd{M-x what-page} counts pages from the beginning of the file, and
counts lines within the page, showing both numbers in the echo area.
@xref{Pages}.

@kindex M-=
@findex count-lines-region
  Use @kbd{M-x count-lines-region} (normally bound to @kbd{M-=}) to
display the number of lines in the region (@pxref{Mark}).  @xref{Pages},
for the command @kbd{C-x l} which counts the lines in the current page.

@kindex C-x =
@findex what-cursor-position
  The command @kbd{C-x =} (@code{what-cursor-position}) shows
information about the current cursor position and the buffer contents
at that position.  It displays a line in the echo area that looks like
this:

@smallexample
Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53
@end smallexample

  After @samp{Char:}, this shows the character in the buffer at point.
The text inside the parenthesis shows the corresponding decimal, octal
and hex character codes; for more information about how @kbd{C-x =}
displays character information, see @ref{International Chars}.  After
@samp{point=} is the position of point as a character count (the first
character in the buffer is position 1, the second character is
position 2, and so on).  The number after that is the total number of
characters in the buffer, and the number in parenthesis expresses the
position as a percentage of the total.  After @samp{column=} is the
horizontal position of point, in columns counting from the left edge
of the window.

  If the buffer has been narrowed, making some of the text at the
beginning and the end temporarily inaccessible, @kbd{C-x =} displays
additional text describing the currently accessible range.  For
example, it might display this:

@smallexample
Char: C (67, #o103, #x43) point=252 of 889 (28%) <231-599> column=0
@end smallexample

@noindent
where the two extra numbers give the smallest and largest character
position that point is allowed to assume.  The characters between
those two positions are the accessible ones.  @xref{Narrowing}.

@node Arguments
@section Numeric Arguments
@cindex numeric arguments
@cindex prefix arguments
@cindex arguments to commands

  In the terminology of mathematics and computing, @dfn{argument}
means ``data provided to a function or operation.''  You can give any
Emacs command a @dfn{numeric argument} (also called a @dfn{prefix
argument}).  Some commands interpret the argument as a repetition
count.  For example, giving @kbd{C-f} an argument of ten causes it to
move point forward by ten characters instead of one.  With these
commands, no argument is equivalent to an argument of one, and
negative arguments cause them to move or act in the opposite
direction.

@kindex M-1
@kindex M-@t{-}
@findex digit-argument
@findex negative-argument
  The easiest way to specify a numeric argument is to type a digit
and/or a minus sign while holding down the @key{META} key.  For
example,

@example
M-5 C-n
@end example

@noindent
moves down five lines.  The keys @kbd{M-1}, @kbd{M-2}, and so on, as
well as @kbd{M--}, are bound to commands (@code{digit-argument} and
@code{negative-argument}) that set up an argument for the next
command.  @kbd{Meta--} without digits normally means @minus{}1.

If you enter more than one digit, you need not hold down the
@key{META} key for the second and subsequent digits.  Thus, to move
down fifty lines, type

@example
M-5 0 C-n
@end example

@noindent
Note that this @emph{does not} insert five copies of @samp{0} and move
down one line, as you might expect---the @samp{0} is treated as part
of the prefix argument.

(What if you do want to insert five copies of @samp{0}?  Type @kbd{M-5
C-u 0}.  Here, @kbd{C-u} ``terminates'' the prefix argument, so that
the next keystroke begins the command that you want to execute.  Note
that this meaning of @kbd{C-u} applies only to this case.  For the
usual role of @kbd{C-u}, see below.)

@kindex C-u
@findex universal-argument
  Instead of typing @kbd{M-1}, @kbd{M-2}, and so on, another way to
specify a numeric argument is to type @kbd{C-u}
(@code{universal-argument}) followed by some digits, or (for a
negative argument) a minus sign followed by digits.  A minus sign
without digits normally means @minus{}1.

  @kbd{C-u} alone has the special meaning of ``four times'': it
multiplies the argument for the next command by four.  @kbd{C-u C-u}
multiplies it by sixteen.  Thus, @kbd{C-u C-u C-f} moves forward
sixteen characters.  Other useful combinations are @kbd{C-u C-n},
@kbd{C-u C-u C-n} (move down a good fraction of a screen), @kbd{C-u
C-u C-o} (make ``a lot'' of blank lines), and @kbd{C-u C-k} (kill four
lines).

  You can use a numeric argument before a self-inserting character to
insert multiple copies of it.  This is straightforward when the
character is not a digit; for example, @kbd{C-u 6 4 a} inserts 64
copies of the character @samp{a}.  But this does not work for
inserting digits; @kbd{C-u 6 4 1} specifies an argument of 641.  You
can separate the argument from the digit to insert with another
@kbd{C-u}; for example, @kbd{C-u 6 4 C-u 1} does insert 64 copies of
the character @samp{1}.

  Some commands care whether there is an argument, but ignore its
value.  For example, the command @kbd{M-q} (@code{fill-paragraph})
fills text; with an argument, it justifies the text as well.
(@xref{Filling}, for more information on @kbd{M-q}.)  For these
commands, it is enough to the argument with a single @kbd{C-u}.

  Some commands use the value of the argument as a repeat count, but
do something special when there is no argument.  For example, the
command @kbd{C-k} (@code{kill-line}) with argument @var{n} kills
@var{n} lines, including their terminating newlines.  But @kbd{C-k}
with no argument is special: it kills the text up to the next newline,
or, if point is right at the end of the line, it kills the newline
itself.  Thus, two @kbd{C-k} commands with no arguments can kill a
nonblank line, just like @kbd{C-k} with an argument of one.
(@xref{Killing}, for more information on @kbd{C-k}.)

  A few commands treat a plain @kbd{C-u} differently from an ordinary
argument.  A few others may treat an argument of just a minus sign
differently from an argument of @minus{}1.  These unusual cases are
described when they come up; they exist to make an individual command
more convenient, and they are documented in that command's
documentation string.

  We use the term ``prefix argument'' as well as ``numeric argument,''
to emphasize that you type these argument before the command, and to
distinguish them from minibuffer arguments that come after the
command.

@node Repeating
@section Repeating a Command
@cindex repeating a command

  Many simple commands, such as those invoked with a single key or
with @kbd{M-x @var{command-name} @key{RET}}, can be repeated by
invoking them with a numeric argument that serves as a repeat count
(@pxref{Arguments}).  However, if the command you want to repeat
prompts for input, or uses a numeric argument in another way, that
method won't work.

@kindex C-x z
@findex repeat
  The command @kbd{C-x z} (@code{repeat}) provides another way to repeat
an Emacs command many times.  This command repeats the previous Emacs
command, whatever that was.  Repeating a command uses the same arguments
that were used before; it does not read new arguments each time.

  To repeat the command more than once, type additional @kbd{z}'s: each
@kbd{z} repeats the command one more time.  Repetition ends when you
type a character other than @kbd{z}, or press a mouse button.

  For example, suppose you type @kbd{C-u 2 0 C-d} to delete 20
characters.  You can repeat that command (including its argument) three
additional times, to delete a total of 80 characters, by typing @kbd{C-x
z z z}.  The first @kbd{C-x z} repeats the command once, and each
subsequent @kbd{z} repeats it once again.