Emacs Lisp: Get universal-argument

This page shows you how to make your emacs lisp command accept Emacs: Universal Argument (prefix arg)

To make your command aware of universal argument, there are 3 simple ways:

• In the function body, check the builtin variable current-prefix-arg. It holds the value of universal argument.

• Add capital P as prompt string to Emacs Lisp: Interactive Form in your function. It passes the value of current-prefix-arg as your function's first parameter.
• Add capital lowercase p as prompt string to Emacs Lisp: Interactive Form in your function. It passes converted numerical value of current-prefix-arg to your function's first argument.

Example:

(defun xf (x)
  "print value of `current-prefix-arg'"
  (interactive "P")
  (message "%s" x))

Possible Values of Universal Argument

Here's the possible values of current-prefix-arg.

(defun xg ()
  "print `current-prefix-arg'"
  (interactive )
  (message "%s" current-prefix-arg))

;; try
;; M-x g
;; C-u M-x g
;; C-u C-u M-x g
;; C-u 1 M-x g
;; C-u 2 M-x g

Convert current-prefix-arg to number

The function prefix-numeric-value converts current-prefix-arg to number.

(defun xh ()
  "print numerical prefix arg received"
  (message "%s" (prefix-numeric-value current-prefix-arg) )
)

Reference

(info "(elisp) Prefix Command Arguments")

• 
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