Emacs: Clean Empty Lines 🚀

By Xah Lee. Date: 2013-02-14. Last updated: 2024-05-27.

Here's 2 commands that remove repeated blank lines and delete trailing white space.

Clean White Space

(defun xah-clean-whitespace ()
  "Delete trailing whitespace, and replace repeated blank lines to just 1.
Only space and tab is considered whitespace here.
Works on whole buffer or selection, respects `narrow-to-region'.

URL `http://xahlee.info/emacs/emacs/elisp_compact_empty_lines.html'
Created: 2017-09-22
Version: 2022-08-06"
  (interactive)
  (let (xbegin xend)
    (if (region-active-p)
        (setq xbegin (region-beginning) xend (region-end))
      (setq xbegin (point-min) xend (point-max)))
    (save-excursion
      (save-restriction
        (narrow-to-region xbegin xend)
        (goto-char (point-min))
        (while (re-search-forward "[ \t]+\n" nil :move) (replace-match "\n"))
        (goto-char (point-min))
        (while (re-search-forward "\n\n\n+" nil :move) (replace-match "\n\n"))
        (goto-char (point-max))
        (while (eq (char-before) 32) (delete-char -1)))))
  (message "%s done" real-this-command))

You can make this automatic. Every time the file is saved, whitespaces are cleaned.

(add-hook 'before-save-hook 'xah-clean-whitespace)

Clean Empty Lines

(defun xah-clean-empty-lines ()
  "Replace repeated blank lines to just 1, in whole buffer or selection.
Respects `narrow-to-region'.

URL `http://xahlee.info/emacs/emacs/elisp_compact_empty_lines.html'
Created: 2017-09-22
Version: 2020-09-08"
  (interactive)
  (let (xbegin xend)
    (if (region-active-p)
        (setq xbegin (region-beginning) xend (region-end))
      (setq xbegin (point-min) xend (point-max)))
    (save-excursion
      (save-restriction
        (narrow-to-region xbegin xend)
        (progn
          (goto-char (point-min))
          (while (re-search-forward "\n\n\n+" nil :move)
            (replace-match "\n\n")))))))

Whitespace Sensitive Files

Be careful on whitespace sensitive language or file format.

For Python, removing trailing whitespace is safe. Compacting empty lines is also safe. (not considering multi-line strings.)
For markdown, removing trailing whitespace will break hard returns <br />. (thanks to Heow Goodman )

If you work with these languages, you probably want to add a check in your function. Try to modify the code. Hint: check on the variable major-mode, or check file name extension.