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4.9 Numeric Arguments
=====================

In mathematics and computer usage, the word "argument" means "data
provided to a function or operation."  Any Emacs command can be given a
"numeric argument" (also called a "prefix argument").  Some commands
interpret the argument as a repetition count.  For example, giving an
argument of ten to the key `C-f' (the command `forward-char', move
forward one character) moves forward ten characters.  With these
commands, no argument is equivalent to an argument of one.  Negative
arguments are allowed.  Often they tell a command to move or act  in
the opposite direction.

   If your keyboard has a <META> key (labelled with a diamond on
Sun-type keyboards and labelled `Alt' on some other keyboards), the
easiest way to specify a numeric argument is to type digits and/or a
minus sign while holding down the <META> key.  For example,
     M-5 C-n
   would move down five lines.  The characters `Meta-1', `Meta-2', and
so on, as well as `Meta--', do this because they are keys bound to
commands (`digit-argument' and `negative-argument') that are defined to
contribute to an argument for the next command.  Digits and `-'
modified with Control, or Control and Meta, also specify numeric
arguments.

   Another way of specifying an argument is to use the `C-u'
(`universal-argument') command followed by the digits of the argument.
With `C-u', you can type the argument digits without holding down
modifier keys; `C-u' works on all terminals.  To type a negative
argument, type a minus sign after `C-u'.  Just a minus sign without
digits normally means -1.

   `C-u' followed by a character which is neither a digit nor a minus
sign has the special meaning of "multiply by four".  It multiplies the
argument for the next command by four.  `C-u' twice multiplies it by
sixteen.  Thus, `C-u C-u C-f' moves forward sixteen characters.  This
is a good way to move forward "fast", since it moves about 1/5 of a line
in the usual size frame.  Other useful combinations are `C-u C-n', `C-u
C-u C-n' (move down a good fraction of a frame), `C-u C-u C-o' (make "a
lot" of blank lines), and `C-u C-k' (kill four lines).

   Some commands care only about whether there is an argument and not
about its value.  For example, the command `M-q' (`fill-paragraph') with
no argument fills text; with an argument, it justifies the text as well.
(Note: Filling, for more information on `M-q'.)  Just `C-u' is a
handy way of providing an argument for such commands.

   Some commands use the value of the argument as a repeat count, but do
something peculiar when there is no argument.  For example, the command
`C-k' (`kill-line') with argument N kills N lines, including their
terminating newlines.  But `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 `C-k' commands with
no arguments can kill a non-blank line, just like `C-k' with an
argument of one.  (Note: Killing, for more information on `C-k'.)

   A few commands treat a plain `C-u' differently from an ordinary
argument.  A few others may treat an argument of just a minus sign
differently from an argument of -1.  These unusual cases are described
when they come up; they are always for reasons of convenience of use of
the individual command.

   You can use a numeric argument to insert multiple copies of a
character.  This is straightforward unless the character is a digit; for
example, `C-u 6 4 a' inserts 64 copies of the character `a'.  But this
does not work for inserting digits; `C-u 6 4 1' specifies an argument
of 641, rather than inserting anything.  To separate the digit to
insert from the argument, type another `C-u'; for example, `C-u 6 4 C-u
1' does insert 64 copies of the character `1'.

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


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