How does one do the reverse of fill-region / fill-paragraph in emacs?

Question

The commands fill-region (and fill-paragraph) breaks lines in a region (and paragraph) to a predefined width. How does one achieve the opposite effect?

Given a buffer, say markdown or org, where paragraphs are separated by two newlines, how does one unfill (remove non-paragraph related line breaks) regions and paragraphs?

There are some hacks to do this, however wanted to know what is the canonical way:

1. Set the variable fill-column to a high value and run fill-paragraph.
2. Use a custom macro.

Answer 1

Try M-x unfill-region and M-x unfill-paragraph. Their documentation says that they are the respective inverses of those two commands.

Edit:

Forgot that this is not built in. You want package unfill from MELPA, or at https://github.com/purcell/unfill

Answer 2

spacemacs has a nice design regarding this in better defaults layer. from it's manual:

Fill or unfill paragraph: Pressing M-q for the first time fills current paragraph and pressing M-q for the second time unfills it.

It achieves this by consulting the last-command variable.

Personly I just use evil's join(J) command, or Emacs's delete-indentation(M-^).

Answer 3

I've been using this from the Emacs wiki:

(defun my-unfill-paragraph (&optional region)
  "Make multi-line paragraph into a single line of text.

REGION unfills the region.  See URL
`https://www.emacswiki.org/emacs/UnfillParagraph'"
  (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)))

It works by setting the upper limit on the fill-column variable to the maximum point in the buffer. The fill-column variable controls the column beyond which automatic line-wrapping should happen. It also sets emacs-lisp-docstring-fill-column to t which means that the fill column for lisp docstrings should use the same fill value as that given by fill-column. In essence, this removes line-wrapping. Finally, it calls the fill command for the region or current paragraph.

Answer 4

I can't think of a quick built-in solution that works in all cases. For a single paragraph, you can:

1. Mark the paragraph (mark-paragraph, M-h).
2. Remove the beginning and ending line break from the region (right C-x C-x left).
3. Replace line breaks by spaces (C-M-% C-q C-j RET SPC RET !).

This is unwieldy enough that setting fill-column to a very high value and running fill-region tends to be more convenient. Doing it for multiple paragraphs is even more unwieldy because there isn't a regular expression that matches line breaks that aren't paragraph breaks.

If you don't want to modify fill-column, you can:

1. Create an indirect buffer: C-x 4 c
2. Set fill-column in the indirect buffer: M-x set-variable RET fill-column RET 99999999 RET
3. (Select what you want and) M-q
4. Close the indirect buffer (C-x k RET C-x 0).