When in javascript mode trying to use C-c C-m i get an error saying "C-c RET is undefined?"
What makes Emacs believe I am pressing RET?
How can i properly make this keybinding work?
- 2Possible duplicate of Properly distinguish Ctrl+i and TabDrew– Drew2016-02-12 13:35:41 +00:00Commented Feb 12, 2016 at 13:35
- 1Same problem, different entry point, I think it would be nice to keep both questions around for people coming from different searches.Jordon Biondo– Jordon Biondo2016-02-12 15:58:14 +00:00Commented Feb 12, 2016 at 15:58
- 1Meta question about whether this question is a duplicateGilles 'SO- stop being evil'– Gilles 'SO- stop being evil'2016-02-14 00:38:33 +00:00Commented Feb 14, 2016 at 0:38
- 1Possible duplicate of How to bind C-i as different from TAB?Gilles 'SO- stop being evil'– Gilles 'SO- stop being evil'2016-02-14 00:39:14 +00:00Commented Feb 14, 2016 at 0:39
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2 Answers
Emacs "thinks" that C-m is RET because "Control M" is the ASCII control character "carriage return". Even though this reason is "historical" Emacs can run in a terminal and so it needs to support the way terminals still work now.
Try opening a terminal window, typing "ls", and pressing C-m. You will see that it is interpreted as "return", even though you are not in Emacs.
See Control character on Wikipedia for details about control characters.
To distinguish C-m from RET in a GUI Emacs, one could change C-i to C-m in @nispio's answer:
(define-key input-decode-map [?\C-m] [C-m]) ;; now we can do this: (defun my-command () (interactive) (message "C-m is not the same as RET any more!")) (global-set-key (kbd "<C-m>") #'my-command) See also
How to distinguish C-i from TAB?, which is very closely related.
How to bind C-i as different from TAB? and this answer in particular.
- 2This is brilliant, thank you. Now I can have
C-mas a prefix map for multiple-cursors.John Wiegley– John Wiegley2017-12-09 18:55:52 +00:00Commented Dec 9, 2017 at 18:55 - How come this issue doesn't show up with the other control characters?user129393192– user1293931922023-07-08 18:01:24 +00:00Commented Jul 8, 2023 at 18:01
I have no idea why, but the accepted answer did not work for me. Maybe it is because of how I declare my key bindings.
I use bind-keys like this...
(bind-keys :map my-mode-map ...) to bind keys, then I activate my-mode so that my key declarations always have precedence. Using my own mode is new, but I always used bind-keys.
In bind-keys I include the following:
([return] . newline) ;; needed to distinguish from C-m Looking at key declaration help, I do not believe that assigning [return] to newline changes the function of the return key, but declaring [return] causes the Return key to become different than Control-M, allowing me to declare [C-m] later in the same bind-keys command and the two declaratoins are unique.
I use the same technique to separate [tab] from [C-i], first binding [tab], then binding [C-i] in the same bind-keys statement.
