Function to copy the whole line if no region is selected

Question

I want to bind this function to M-w, so that it copies the region if one is selected, otherwise it copies the whole line silently, without having any other side-effects like moving the cursor to some other places.

I saw some examples, but they all do some additional stuff that I don't like, like moving the cursor to the next line.

I'm not an expert in Elisp, but some functions I saw might be buggy, because their bodies contain "\n", to refer to "newline", which is obviously wrong, because not all systems use this convention.

Answer 1

To avoid side effects like moving the point (that is, the cursor), wrap your movement commands in save-excursion. Prior Emacs 25 this also saved the mark (the other end of the selected region). Now to save the mark as well use save-mark-and-excursion.

First we need a function to select the whole line:

(defun mark-whole-line ()
  (beginning-of-line)
  (set-mark-command nil)
  (end-of-line))

This function moves the point and the mark.

Now we need to know if the region is active. The function region-active-p does this. Now just check the state of the region and use an if/then to either call the normal function M-w is bound to or save the state, use the above function to mark the whole line and then copy it:

(defun kill-ring-save-whole-line-or-region ()
  (interactive)
  (if (region-active-p)
      (call-interactively #'kill-ring-save) ;; then
    (save-mark-and-excursion ;; else
      (mark-whole-line)
      (kill-ring-save (region-beginning) (region-end))
      (pop-mark)
      )))

Finally to bind it to a key: (define-key global-map (kbd "M-w") #'kill-ring-save-whole-line-or-region)

Answer 2

You want the whole-line-or-region package. With whole-line-or-region-local-mode activated, things like C-w and M-w Do The Right Thing on the current line when then is no active region.