'By Emacs, how to join two lines into one?

I am new to Emacs. I have googled this but no good answer there. One of them is Ctrl-n Ctrl-a Backspace This works but is stupid. Is there a quick and simple way to join a block of lines into a single line?

Actually, I can use Esc-q to auto-fill a paragraph now, but how could I get it to revert without UNDO?

emacs editor

Solution 1:^[1]

Place point anywhere on the last line of the group of lines that need joining and call

M-^

repeatedly until all the lines are merged.

Note: It leaves one space between all of the now joined lines.

Solution 2:^[2]

M-x join-line will join two lines. Just bind it to a convenient keystroke.

Solution 3:^[3]

Multiple Cursors combined with M-^ will collapse all selected lines into one with all extraneous white-space removed.

For example to select an entire buffer, invoke multiple cursors mode, collapse into one line, and then disable multiple cursors mode:

C-x h
M-x mc/edit-lines
M-^
C-g

Solution 4:^[4]

The Emacs conventional name for "join" is "fill". Yes, you can join two lines with M-^ -- and that's handy -- but more generally you'll want to join n lines. For this, see the fill* commands, such as fill-region, fill-paragraph, etc.

See this for more info on selecting things which can then be filled.

Also, you can join multiple lines with M-^ by selecting those lines first. (Note that the universal argument does not work with this.)

Solution 5:^[5]

Just replace newlines with nothing.

Solution 6:^[6]

I like the way Sublime text Join line with Command J so I do it this way:

(defun join-lines (arg)
  (interactive "p")
  (end-of-line)
  (delete-char 1)
  (delete-horizontal-space)
  (insert " "))

Solution 7:^[7]

I use the following function and bind it to 'M-J'.

(defun concat-lines ()
  (interactive)
  (next-line)
  (join-line)
  (delete-horizontal-space))

If you prefer to keep your cursor position, you can use save-excursion.

Solution 8:^[8]

The most simplest way ever:

Select paragraph/lines by M-h or C-SPC

Press M-q

Witness the Emagics (Emacs Magic)!!

Solution 9:^[9]

Because join-line will left one space between two lines, also it only support join two lines. In case of you want to join plenty of lines without one space left, you can use "search-replace" mode to solve, as follows:

C-%
Query: input C-q C-j Enter
Replace: Enter
Run the replacement. Enter

Done.

Solution 10:^[10]

"how could I get it to revert without UNDO?":

(defun toggle-fill-paragraph ()
  ;; Based on http://xahlee.org/emacs/modernization_fill-paragraph.html
  "Fill or unfill the current paragraph, depending upon the current line length.
When there is a text selection, act on the region.
See `fill-paragraph' and `fill-region'."
  (interactive)
  ;; We set a property 'currently-filled-p on this command's symbol
  ;; (i.e. on 'toggle-fill-paragraph), thus avoiding the need to
  ;; create a variable for remembering the current fill state.
  (save-excursion
    (let* ((deactivate-mark nil)
           (line-length (- (line-end-position) (line-beginning-position)))
           (currently-filled (if (eq last-command this-command)
                                 (get this-command 'currently-filled-p)
                               (< line-length fill-column)))
           (fill-column (if currently-filled
                            most-positive-fixnum
                          fill-column)))
      (if (region-active-p)
          (fill-region (region-beginning) (region-end))
        (fill-paragraph))
      (put this-command 'currently-filled-p (not currently-filled)))))
(global-set-key (kbd "M-q") 'toggle-fill-paragraph)

Solution 11:^[11]

From EmacsWiki: Unfill Paragraph

 ;;; Stefan Monnier <foo at acm.org>. It is the opposite of fill-paragraph    
    (defun unfill-paragraph (&optional region)
      "Takes a multi-line paragraph and makes it into a single line of text."
      (interactive (progn (barf-if-buffer-read-only) '(t)))
      (let ((fill-column (point-max))
            ;; This would override `fill-column' if it's an integer.
            (emacs-lisp-docstring-fill-column t))
        (fill-paragraph nil region)))

Solution 12:^[12]

A basic join of 2 lines:

(delete-indentation)

I like to line below to be joined to the current without moving the cursor:

("C-j" .
  (lambda (iPoint)
    "Join next line onto current line"
    (interactive "d")
    (next-line)
    (delete-indentation)
    (goto-char iPoint)))

Solution 13:^[13]

This one behaves like in vscode. So it add space only if join line consisted something else than whitespace. And I bind it to alt+shift+j.

Shorter version based on crux-top-join-line:

(global-set-key (kbd "M-J") (lambda () (interactive) (delete-indentation 1)))

Longer version based on https://stackoverflow.com/a/33005183/588759.

;; https://stackoverflow.com/questions/1072662/by-emacs-how-to-join-two-lines-into-one/68685485#68685485
(defun join-lines ()
  (interactive)
  (next-line)
  (join-line)
  (delete-horizontal-space)
  (unless (looking-at-p "\n") (insert " ")))

(global-set-key (kbd "M-J") 'join-lines)

Solution 14:^[14]

Two ways come to mind:

Once you think of it, the most obvious (or at least easiest to remember) way is to use M-q format-paragraph with a long line length C-x-f 1000.
There is also a built-in tool M-^ join-line. More usefully, if you select a region then it will combine them all into one line.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	Ray
Solution 2	pgs
Solution 3	huntar
Solution 4
Solution 5	Tal Pressman
Solution 6	Mark
Solution 7	Community
Solution 8
Solution 9	user5698801
Solution 10	CodyChan
Solution 11	Marduk
Solution 12	Paul
Solution 13
Solution 14	Raymond Hettinger

'By Emacs, how to join two lines into one?

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