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Most of the convenient OS X keybindings that GNU Emacs defines, such as s-a for C-x h, are not all that useful to me. I'd like to make Super synonymous with Ctrl. Is there a way to easily map all key chords involving Super to the equivalent Ctrl version? Failing that, is there a way to map a key to another key that works for prefix keys as well as non-prefix keys?

I've tried using keyboard-translate and global-set-key so far.

(keyboard-translate (kbd "s-a") (kbd "C-a")) results in a type error. I'm not sure why.

(global-set-key (kbd "s-a") (kbd "C-a")) works fine, but (global-set-key (kbd "s-h") (kbd "C-h")) does not seem to do much of anything.

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    If you are using the GUI version of Emacs instead of the terminal, then perhaps this answer will help: stackoverflow.com/a/34933409/2112489 You can modify it as you see fit. For any variable listed, just type M-x describe-variable or C-h v to learn more about the available options.
    – lawlist
    Nov 28, 2016 at 7:18
  • That does solve the immediate problem, but I'm a little curious why keyboard-translate didn't work as intended and why using global-set-key and the like works differently for prefix keys. It might be more appropriate to structure those as separate questions or hunt around more, I'm not sure.
    – Greg Nisbet
    Nov 28, 2016 at 7:24
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    Another forum participant will need to help with keyboard-translate as I've never used it. I have set up my own keyboard shortcuts and disabled those that I didn't find useful, so I have no need to remap anything. Sorry that I couldn't be of more assistance.
    – lawlist
    Nov 28, 2016 at 7:27

2 Answers 2

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So I think:

(keyboard-translate (kbd "s-a") (kbd "C-a"))

results in a type error because keyboard-translate takes character parameters, but kbd returns an "internal Emacs key representation", something very different than a character.

Also I don't think your use of global-set-key is doing what you think it's doing: when you say (global-set-key (kbd "s-a") (kbd "C-a")), you are actually binding the key s-a to the output of the command (kbd "C-a"). Apparently (surprisingly, to me) that happens to do what you meant for a single-key command, but it makes sense to me that it wouldn't work at all for prefix-map keybindings.

As lawlist said in the link in their comment, setting ns-command-modifier is the way to do what you want here.

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  • I still don't follow why (kbd "C-a") doesn't give do what I want in the case of prefix keys. I thought that kbd just maps from a human-readable string notation for sequence of keys to an internal representation that makes sense to emacs. I guess the fundamental question here is why mapping a key to a key works in some cases but not others. I still don't have a good intuition there. I've been using the ns-command-modifier workaround for the past few months and haven't had any problems with it.
    – Greg Nisbet
    Feb 7, 2017 at 4:30
  • OK, so for prefix commands, e.g. C-h is bound to a special value that says it can be used as a prefix. When you (global-set-key (kbd "s-h") (kbd "C-h")), you aren't binding S-h as a prefix key, you are binding it to the output of (kbd "C-h"), which is just a string. So striking S-h will invoke a string, which doesn't do anything. Does that make sense?
    – Willy Lee
    Feb 7, 2017 at 5:28
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Adding another option in case someone is looking for different solutions.

If the Super => Control mapping is only desired in GUI Emacs (on macOS), one can use Karabiner Elements (FOSS) with the appropriate "complex modification." These are the steps:

  1. Put this in a file, like super_to_control_on_emacs.json:

    { "title": "Super to Ctrl on Emacs",
  "rules": [
    { "description": "Turn Command (Super) into Ctrl on Emacs",
      "manipulators": [
        { "type": "basic",
          "from": { "key_code": "left_command",
                    "modifiers": { "optional": ["any"] } },
          "to": [ { "key_code": "left_control" } ],
          "conditions": [ { "type": "frontmost_application_if",
                            "bundle_identifiers": ["^org\\.gnu\\.Emacs$"] } ] },
        { "type": "basic",
          "from": { "key_code": "right_command",
                    "modifiers": { "optional": ["any"] }},
          "to": [ { "key_code": "right_control" } ],
          "conditions": [ { "type": "frontmost_application_if",
                            "bundle_identifiers": [ "^org\\.gnu\\.Emacs$" ] } ] } ] } ] }

  2. Copy it to ~/.config/karabiner/assets/complex_modifications/

  3. Open Karabiner Elements > Complex Modifications > Add Rule > Turn Command (Super) into Ctrl on Emacs > Enable. That's it!

This template can be used for other Emacs-specific modifications as well.

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