Duplicating the current line is frequent editing for me when I am coding. Initially, I copied a snippet as a command in Emacs from the Internet:
(defun w/duplicate-line()
"Duplicate the current line."
(interactive)
(move-beginning-of-line 1)
(kill-line)
(yank)
(open-line 1)
(next-line 1)
(yank))Most of the time, I was happy with it, but it has mainly two drawbacks:
- It cannot keep the column position when moving to the next line
- It messes up with the yank ring as it yanks the text under the hood
So today, I took some time to fix these two problems, and I also want it to be capable of commenting the current line out if I prefix the command.
Here is the improved version (it still doesn't handle the column position perfectly when the user commenting on the line first, but I am ok with it):
(defun w/duplicate-line(comment-first)
"Duplicate the current line."
(interactive "P")
(let ((line-text (buffer-substring-no-properties
(line-beginning-position)
(line-end-position))))
(save-excursion
(if comment-first
(progn
(comment-line 1)
(move-beginning-of-line 1)
(open-line 1))
(move-end-of-line 1)
(open-line 1)
(forward-char))
(insert line-text))
(next-line)))
Update: Interestingly, Lars Ingebrigtsen also introduced a duplicate-line command to Emacs 29 recently, see discussions on this emacs-devel thread.