(defun untabify (start end)
"Convert all tabs in region to multiple spaces, preserving columns.
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 "r")
(save-excursion
(save-restriction
(narrow-to-region (point-min) end)
(goto-char start)
(while (search-forward "\t" nil t) (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))))))
(defvar tabify-regexp " [ \t]+"
"Regexp matching whitespace that tabify should consider.
Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
\"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")
(defun tabify (start end)
"Convert multiple spaces in region to tabs when possible.
A group of spaces is partially replaced by tabs
when this can be done without changing the column they end at.
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 "r")
(save-excursion
(save-restriction
(goto-char start)
(beginning-of-line)
(narrow-to-region (point) end)
(goto-char start)
(let ((indent-tabs-mode t))
(while (re-search-forward tabify-regexp nil t)
(let ((end-col (current-column))
(beg-col (save-excursion (goto-char (match-beginning 0))
(skip-chars-forward "\t")
(current-column))))
(if (= (/ end-col tab-width) (/ beg-col tab-width))
nil
(delete-region (match-beginning 0) (point))
(indent-to end-col))))))))
(provide 'tabify)