• Context: using Emacs 26.2

I would like to write Emacs Lisp code that inserts or over-types text depending of the state of the overwrite-mode. I would call this function to insert text instead of the standard insert function. When code uses the standard insert function while overwrite-mode is t, text is inserted and not overwritten.

I could write and use the following function, but I would have thought that such functionality would already be built-in Emacs. I can't find it. Does Emacs already provide a similar function?

(defun insert-or-overwrite (text)
  "Insert or overwrite text depending of overwrite-mode status."
  (when overwrite-mode
    (delete-char (length text)))
  (insert text))
  • Do you know why? Is it because it's difficult to handle all cases?
    – PRouleau
    Jul 27, 2020 at 21:11

1 Answer 1


The answer is almost yes. self-insert-command is the command that is run for those keys that simply insert a character into the current buffer, and it handles overwrite correctly (and it handles the edge cases that you have forgotten in the code you wrote; I recommend taking a look at it yourself). Of course it's not really very convenient to use, since it doesn't take a string of text as an argument.

  • Thanks. I know my code does not handle a single character. It should check for it as in: (defun insert-or-overwrite (text) "Insert or overwrite text depending of overwrite-mode status." (when overwrite-mode (if (stringp text) (delete-char (length text)) (delete-char 1))) (insert text)) --- However I can't see how to invoke self-insert-command from code and pass it a string. How would you call it to insert a single character? And it's written in C, so that's not really an option unless I contribute one directly in Emacs.
    – PRouleau
    Jul 27, 2020 at 20:57
  • I suppose that could be an edge case, if your function were called with a char instead of a string, but note carefully how self-insert-command handles double-wide characters, in both the input and the buffer.
    – db48x
    Jul 27, 2020 at 21:01
  • I didn't think of multi-byte characters. But even for non-ASCII, it only works for strings not characters. I just tried it with as an input and I got it failing sequencep (223). However attempting to overwrite "-ß-" worked fine.
    – PRouleau
    Jul 27, 2020 at 21:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.