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 number of commands to perform this in Emacs?

Answer 1

In addition to the previous answers you can also define your own function to duplicate a line. For example, putting the following in your .emacs file will make C-d duplicate the current line.

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

Answer 2

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 3

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 4

install duplicate-thing from melpa

and add this keybinding:

(global-set-key (kbd "M-c") 'duplicate-thing)

Answer 5

With prefix arguments, and what is (I hope) intuitive behaviour:

(defun duplicate-line (&optional arg)
  "Duplicate it. With prefix ARG, duplicate ARG times."
  (interactive "p")
  (next-line 
   (save-excursion 
     (let ((beg (line-beginning-position))
           (end (line-end-position)))
       (copy-region-as-kill beg end)
       (dotimes (num arg arg)
         (end-of-line) (newline)
         (yank))))))

The cursor will remain on the last line. Alternatively, you might want to specify a prefix to duplicate the next few lines at once:

(defun duplicate-line (&optional arg)
  "Duplicate it. With prefix ARG, duplicate ARG times."
  (interactive "p")
  (save-excursion 
    (let ((beg (line-beginning-position))
          (end 
           (progn (forward-line (1- arg)) (line-end-position))))
      (copy-region-as-kill beg end)
      (end-of-line) (newline)
      (yank)))
  (next-line arg))

I find myself using both often, using a wrapper function to switch the behavior of the prefix argument.

And a keybinding: (global-set-key (kbd "C-S-d") 'duplicate-line)

Answer 6

@[Kevin Conner]: Pretty close, so far as I know. The only other thing to consider is turning on kill-whole-line to include the newline in the C-k.