GNU Emacs Lisp Reference Manual

29.19: Substituting for a Character Code

The following functions replace characters within a specified region based on their character codes.

Function: subst-char-in-region start end old-char new-char &optional noundo

This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.

If noundo is non-nil, then subst-char-in-region does not record the change for undo and does not mark the buffer as modified. This feature is used for controlling selective display (see Selective Display).

subst-char-in-region does not move point and returns nil.

---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
(subst-char-in-region 1 20 ?i ?X)
     => nil

---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------

Function: translate-region start end table

This function applies a translation table to the characters in the buffer between positions start and end.

The translation table table is a string; (aref table ochar) gives the translated character corresponding to ochar. If the length of table is less than 256, any characters with codes larger than the length of table are not altered by the translation.

The return value of translate-region is the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table.