Emacs: Clean Empty Lines 🚀

By Xah Lee. Date: 2013-02-14. Last updated: 2020-09-08.

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 text selection, respects `narrow-to-region'.

URL `http://xahlee.info/emacs/emacs/elisp_compact_empty_lines.html'
Version 2017-09-22 2020-09-08"
  (interactive)
  (let ($begin $end)
    (if (use-region-p)
        (setq $begin (region-beginning) $end (region-end))
      (setq $begin (point-min) $end (point-max)))
    (save-excursion
      (save-restriction
        (narrow-to-region $begin $end)
        (progn
          (goto-char (point-min))
          (while (re-search-forward "[ \t]+\n" nil "move")
            (replace-match "\n")))
        (progn
          (goto-char (point-min))
          (while (re-search-forward "\n\n\n+" nil "move")
            (replace-match "\n\n")))
        (progn
          (goto-char (point-max))
          (while (equal (char-before) 32) ; char 32 is space
            (delete-char -1))))
      (message "white space cleaned"))))

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.
Works on whole buffer or text selection, respects `narrow-to-region'.

URL `http://xahlee.info/emacs/emacs/elisp_compact_empty_lines.html'
Version 2017-09-22 2020-09-08"
  (interactive)
  (let ($begin $end)
    (if (use-region-p)
        (setq $begin (region-beginning) $end (region-end))
      (setq $begin (point-min) $end (point-max)))
    (save-excursion
      (save-restriction
        (narrow-to-region $begin $end)
        (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.