emacs: Arguments
7.10 Numeric Arguments
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In the terminology of mathematics and computing, “argument” means “data
provided to a function or operation”. You can give any Emacs command a
“numeric argument” (also called a “prefix argument”). Some commands
interpret the argument as a repetition count. For example, giving ‘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.
The easiest way to specify a numeric argument is to type a digit
and/or a minus sign while holding down the <META> key. For example,
M-5 C-n
moves down five lines. The keys ‘M-1’, ‘M-2’, and so on, as well as
‘M--’, are bound to commands (‘digit-argument’ and ‘negative-argument’)
that set up an argument for the next command. ‘M--’ without digits
normally means −1.
If you enter more than one digit, you need not hold down the <META>
key for the second and subsequent digits. Thus, to move down fifty
lines, type
M-5 0 C-n
Note that this _does not_ insert five copies of ‘0’ and move down one
line, as you might expect—the ‘0’ is treated as part of the prefix
argument.
(What if you do want to insert five copies of ‘0’? Type ‘M-5 C-u 0’.
Here, ‘C-u’ terminates the prefix argument, so that the next keystroke
begins the command that you want to execute. Note that this meaning of
‘C-u’ applies only to this case. For the usual role of ‘C-u’, see
below.)
Instead of typing ‘M-1’, ‘M-2’, and so on, another way to specify a
numeric argument is to type ‘C-u’ (‘universal-argument’) followed by
some digits, or (for a negative argument) a minus sign followed by
digits. A minus sign without digits normally means −1.
‘C-u’ alone has the special meaning of “four times”: it multiplies
the argument for the next command by four. ‘C-u C-u’ multiplies it by
sixteen. Thus, ‘C-u C-u C-f’ moves forward sixteen characters. Other
useful combinations are ‘C-u C-n’, ‘C-u C-u C-n’ (move down a good
fraction of a screen), ‘C-u C-u C-o’ (make sixteen blank lines), and
‘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, ‘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. You can separate the argument from
the digit to insert with another ‘C-u’; for example, ‘C-u 6 4 C-u 1’
does insert 64 copies of the character ‘1’.
Some commands care whether there is an argument, but ignore its
value. For example, the command ‘M-q’ (‘fill-paragraph’) fills text;
with an argument, it justifies the text as well. (
Filling, for
more information on ‘M-q’.) For these commands, it is enough to specify
the argument with a single ‘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
‘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 nonblank line, just like ‘C-k’ with an argument of
one. (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 exist to make an individual command more
convenient, and they are documented in that command’s documentation
string.
We use the term “prefix argument” to emphasize that you type such
arguments before the command, and to distinguish them from minibuffer
arguments (Minibuffer), which are entered after invoking the
command.
Info Catalog
emacs: Position Info
emacs: Basic
emacs: Repeating