Mine's with a region.

(defun comment-and-duplicate-region (start end)
  (interactive "r")
  (let ((s (buffer-substring start end)))
    (comment-region start end)
    (beginning-of-line)
    (save-excursion (insert s))))


On Sun, Jan 17, 2010 at 6:37 AM, Dirk-Jan C. Binnema <djcb.bulk@gmail.com>wrote:

> Hi,
>
> >>>>> "alin" == alin s <alinsoar@voila.fr> writes:
>
>    alin> For me it would be very convenient to have a key-binding to
> duplicate the
>    alin> current line.
>
>    alin> In order to duplicate it I have to press
>
>    alin> C-a C-SPACE C-e C-f M-w C-g C-y
>
>    alin> It's too much for an usual function. C-x C-a would be good?
>
>
> I like 'slick copy', ie., copy without needing to select:
>
> http://emacs-fu.blogspot.com/2009/11/copying-lines-without-selecting-them.html
>
> Then, you can duplicate lines with:
>
>  M-w C-y
>
> Which is very natural.
>
>
>    alin> More than that, if I press C-u C-x C-a, I wish to duplicate the
> current
>    alin> line, and to comment the old line.
>
>    alin> Do you consider that such a function would be useful for many of
> you?
>    alin> Otherwise, I have to wtite it myseld in my own .emacs...
>
> Something quick and fairly dirty:
>
> (defun comment-and-dup ()
>  (interactive)
>  (save-excursion
>    (beginning-of-line)
>    (push-mark)
>    (forward-line 1)
>    (let ((str (buffer-substring (region-beginning) (region-end))))
>      (comment-region (region-beginning) (region-end))
>      (next-line)
>      (insert-string str))))
>
> Best wishes,
> Dirk.
>
> --
> Dirk-Jan C. Binnema                  Helsinki, Finland
> e:djcb@djcbsoftware.nl <e%3Adjcb@djcbsoftware.nl>           w:
> www.djcbsoftware.nl
> pgp: D09C E664 897D 7D39 5047 A178 E96A C7A1 017D DA3C
>
>
>