Function: untabify

untabify is an autoloaded, interactive and byte-compiled function defined in tabify.el.gz.

Signature

(untabify START END &optional ARG)

Documentation

Convert all tabs in region to multiple spaces, preserving columns.

If called interactively with prefix ARG, convert for the entire buffer.

Called non-interactively, the region is specified by arguments START and END, rather than by the position of point and mark. The variable tab-width controls the spacing of tab stops.

View in manual

Probably introduced at or before Emacs version 21.1.

Key Bindings

Source Code

;; Defined in /usr/src/emacs/lisp/tabify.el.gz
;;; tabify.el --- tab conversion commands for Emacs  -*- lexical-binding: t -*-

;; Copyright (C) 1985, 1994, 2001-2025 Free Software Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org
;; Package: emacs

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Commands to optimize spaces to tabs or expand tabs to spaces in a region
;; (`tabify' and `untabify').  The variable tab-width does the obvious.

;;; Code:

;;;###autoload
(defun untabify (start end &optional _arg)
  "Convert all tabs in region to multiple spaces, preserving columns.
If called interactively with prefix ARG, convert for the entire
buffer.

Called non-interactively, the region is specified by arguments
START and END, rather than by the position of point and mark.
The variable `tab-width' controls the spacing of tab stops."
  (interactive (if current-prefix-arg
		   (list (point-min) (point-max) current-prefix-arg)
		 (list (region-beginning) (region-end) nil)))
  (let ((c (current-column)))
    (save-excursion
      (save-restriction
        (narrow-to-region (point-min) end)
        (goto-char start)
        (while (search-forward "\t" nil t)      ; faster than re-search
          (forward-char -1)
          (let ((tab-beg (point))
                (indent-tabs-mode nil)
                column)
            (skip-chars-forward "\t")
            (setq column (current-column))
            (delete-region tab-beg (point))
            (indent-to column)))))
    (move-to-column c)))