Running Commands by Name
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The Emacs commands that are used often or that must be quick to type are bound to keys---short sequences of characters---for convenient use.  Other Emacs commands that are used more rarely are not bound to keys; to run them, you must refer to them by name.

A command name consists, by convention, of one or more words, separated by hyphens: for example, auto-fill-mode or manual-entry.  The use of English words makes the command name easier to remember than a key made up of obscure characters, even though it results in more characters to type.  You can run any command by name, even if it can be run by keys as well.

To run a command by name, start with M-x, then type the command name, and finish with RET.  M-x uses the minibuffer to read the command name.  RET exits the minibuffer and runs the command.

Emacs uses the minibuffer for reading input for many different purposes; on this occasion, the string M-x is displayed at the beginning of the minibuffer as a prompt to remind you that your input should be the name of a command to be run.  See Minibuffer, for full information on the features of the minibuffer.

You can use completion to enter a command name.  For example, to invoke the command forward-char, type:

     M-x forward-char RET

or

     M-x fo TAB c RET

After you type in M-x fo TAB emacs will give you a possible list of completions from which you can choose. Note that forward-char is the same command that you invoke with the key C-f.  You can call any command (interactively callable function) defined in Emacs by its name using M-x regardless of whether or not any keys are bound to it.

If you type C-g while Emacs reads the command name, you cancel the M-x command and get out of the minibuffer, ending up at top level.

To pass a numeric argument to a command you are invoking with M-x, specify the numeric argument before the M-x.  M-x passes the argument along to the function that it calls.  The argument value appears in the prompt while the command name is being read.

You can use the command M-x interactive to specify a way of parsing arguments for interactive use of a function.  For example, write:

       (defun foo (arg) "Doc string" (interactive "p") ...use arg...)

to make arg be the prefix argument when foo is called as a command.  The call to interactive is actually a declaration rather than a function; it tells call-interactively how to read arguments to pass to the function.  When actually called, interactive returns nil.

The argument of INTERACTIVE is usually a string containing a code letter followed by a prompt.  Some code letters do not use I/O to get the argument and do not need prompts.  To prompt for multiple arguments, you must provide a code letter, its prompt, a newline, and another code letter, and so forth.  If the argument is not a string, it is evaluated to get a list of arguments to pass to the function.  If you do not provide an argument to interactive, no arguments are passed when calling interactively.

Available code letters are:

a
     Function name: symbol with a function definition

b
     Name of existing buffer

B
     Name of buffer, possibly nonexistent

c
     Character

C
     Command name: symbol with interactive function definition

d
     Value of point as number (does not do I/O)

D
     Directory name

e
     Last mouse event

f
     Existing file name

F
     Possibly nonexistent file name

k
     Key sequence (string)

m
     Value of mark as number (does not do I/O)

n
     Number read using minibuffer

N
     Prefix arg converted to number, or if none, do like code n

p
     Prefix arg converted to number (does not do I/O)

P
     Prefix arg in raw form (does not do I/O)

r
     Region: point and mark as two numeric arguments, smallest first (does not do I/O)

s
     Any string

S
     Any symbol

v
     Variable name: symbol that is user-variable-p

x
     Lisp expression read but not evaluated

X
     Lisp expression read and evaluated

In addition, if the string begins with *, an error is signaled if the buffer is read-only.  This happens before reading any arguments.  If the string begins with @, the window the mouse is over is selected before anything else is done.  You may use both @ and *; they are processed in the order that they appear.

Normally, when describing a command that is run by name, we omit the RET that is needed to terminate the name.  Thus we may refer to M-x auto-fill-mode rather than M-x auto-fill-mode RET. We mention the RET only when it is necessary to emphasize its presence, for example, when describing a sequence of input that contains a command name and arguments that follow it.

M-x is defined to run the command execute-extended-command, which is responsible for reading the name of another command and invoking it.