How do I duplicate a whole line in Emacs?

Question

I saw this same question for VIM and it has been something that I myself wanted to know how to do for Emacs. In ReSharper I use CTRL-D for this action. What is the least num

Answer 1

When called interactively with no active region, COPY (M-w) a single line instead :

(defadvice kill-ring-save (before slick-copy activate compile)
  "When called interactively with no active region, COPY a single line instead."
  (interactive
   (if mark-active (list (region-beginning) (region-end))
     (message "Copied line")
     (list (line-beginning-position)
           (line-beginning-position 2)))))

When called interactively with no active region, KILL (C-w) a single line instead.

(defadvice kill-region (before slick-cut activate compile)
  "When called interactively with no active region, KILL a single line instead."
  (interactive
   (if mark-active (list (region-beginning) (region-end))
     (message "Killed line")
     (list (line-beginning-position)
           (line-beginning-position 2)))))

Also, on a related note:

(defun move-line-up ()
  "Move up the current line."
  (interactive)
  (transpose-lines 1)
  (forward-line -2)
  (indent-according-to-mode))

(defun move-line-down ()
  "Move down the current line."
  (interactive)
  (forward-line 1)
  (transpose-lines 1)
  (forward-line -1)
  (indent-according-to-mode))

(global-set-key [(meta shift up)]  'move-line-up)
(global-set-key [(meta shift down)]  'move-line-down)

Answer 2

I cannot believe all these complicated solutions. This is two keystrokes:

<C-S-backspace> runs the command kill-whole-line

C-/ runs the command undo

So <C-S-backspace> C-/ to "copy" a whole line (kill and undo).

You can, of course, combine this with numeric and negative args to kill multiple lines either forward or backward.

Answer 3

Nathan's addition to your .emacs file is the way to go but it could be simplified slightly by replacing

  (open-line 1)
  (next-line 1)

with

  (newline)

yielding

(defun duplicate-line()
  (interactive)
  (move-beginning-of-line 1)
  (kill-line)
  (yank)
  (newline)
  (yank)
)
(global-set-key (kbd "C-d") 'duplicate-line)

Answer 4

I liked FraGGod's version, except for two things: (1) It doesn't check whether the buffer is already read-only with (interactive "*"), and (2) it fails on the last line of the buffer if that last line is empty (as you cannot kill the line in that case), leaving your buffer read-only.

I made the following changes to resolve that:

(defun duplicate-line ()
  "Clone line at cursor, leaving the latter intact."
  (interactive "*")
  (save-excursion
    ;; The last line of the buffer cannot be killed
    ;; if it is empty. Instead, simply add a new line.
    (if (and (eobp) (bolp))
        (newline)
      ;; Otherwise kill the whole line, and yank it back.
      (let ((kill-read-only-ok t)
            deactivate-mark)
        (toggle-read-only 1)
        (kill-whole-line)
        (toggle-read-only 0)
        (yank)))))

Answer 5

This functionality should match up with JetBrains' implementation in terms of duplicating both by line or region, and then leaving the point and/ or active region as expected:

Just a wrapper to around the interactive form:

(defun wrx/duplicate-line-or-region (beg end)
  "Implements functionality of JetBrains' `Command-d' shortcut for `duplicate-line'.
   BEG & END correspond point & mark, smaller first
   `use-region-p' explained: 
   http://emacs.stackexchange.com/questions/12334/elisp-for-applying-command-to-only-the-selected-region#answer-12335"
  (interactive "r")
  (if (use-region-p)
      (wrx/duplicate-region-in-buffer beg end)
    (wrx/duplicate-line-in-buffer)))

Which calls this,

(defun wrx/duplicate-region-in-buffer (beg end)
  "copy and duplicate context of current active region
   |------------------------+----------------------------|
   |        before          |           after            |
   |------------------------+----------------------------|
   | first <MARK>line here  | first line here            |
   | second item<POINT> now | second item<MARK>line here |
   |                        | second item<POINT> now     |
   |------------------------+----------------------------|
   TODO: Acts funky when point < mark"
  (set-mark-command nil)
  (insert (buffer-substring beg end))
  (setq deactivate-mark nil))

Or this

(defun wrx/duplicate-line-in-buffer ()
  "Duplicate current line, maintaining column position.
   |--------------------------+--------------------------|
   |          before          |          after           |
   |--------------------------+--------------------------|
   | lorem ipsum<POINT> dolor | lorem ipsum dolor        |
   |                          | lorem ipsum<POINT> dolor |
   |--------------------------+--------------------------|
   TODO: Save history for `Cmd-Z'
   Context: 
   http://stackoverflow.com/questions/88399/how-do-i-duplicate-a-whole-line-in-emacs#answer-551053"
  (setq columns-over (current-column))
  (save-excursion
    (kill-whole-line)
    (yank)
    (yank))
  (let (v)
    (dotimes (n columns-over v)
      (right-char)
      (setq v (cons n v))))
  (next-line))

And then I have this bound to meta+shift+d

(global-set-key (kbd "M-D") 'wrx/duplicate-line-or-region)

Answer 6

something you might want to have in your .emacs is

(setq kill-whole-line t)

Which basically kills the entire line plus the newline whenever you invoke kill-line (i.e. via C-k). Then without extra code, you can just do C-a C-k C-y C-y to duplicate the line. It breaks down to

C-a go to beginning of line
C-k kill-line (i.e. cut the line into clipboard)
C-y yank (i.e. paste); the first time you get the killed line back; 
    second time gives the duplicated line.

But if you use this often then maybe a dedicated key binding might be a better idea, but the advantage of just using C-a C-k C-y C-y is you can duplicate the line elsewhere, instead of just below the current line.