How to remap two keys to another combo with two keys

Question

I'm using a Mac Mini running Catalina with a Logitech K270 keyboard, with Karabiner 12.10.0. I've done some simple key changes, I work with latex, where the backslash symbol is written a lot, I get " \ " backslash with AltGr ("right_option") + < > ("non_us_backslash") keys, I prefer use the combo: AltGr ("right_option") + \ ("grave_accent_and_tilde"). I have in the karabiner.json:

    "rules": [
                    {
                        "description": "Barra Invertida",
                        "manipulators": [
                            {
                                "from": {
                                    "key_code": "non_us_backslash",
                                    "modifiers": "right_option"
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "grave_accent_and_tilde",
                                        "modifiers": "right_option"
                                    }
                                ],
                                "type": "basic"
                            }
                        ]
                    }
                ]
            },

But I can't get the backslash symbol.

Any suggestions? Can it be remapped to a single key?

Answer 1

First, if you use modifiers in a "from": context they need either be "mandatory" (as probable in your case) or "optional" (if allowed but not necessary). Your "from": line therefore must be expanded to:

"from": { "key_code": "non_us_backslash",
          "modifiers": { "mandatory": ["right_option"] }
        }

Further, I (can only) suspect that actually you want to press
right_option + grave_accent_and_tilde in order to print a \ char.

In this case right_option + non_us_backslash is actually NOT your "from": but your goal –
you want to press a "fresh" combo that tells Karabiner to press an "unwanted" one for you.

Your code (in part) should read:

"from": {
    "key_code": "grave_accent_and_tilde",
    "modifiers": { "mandatory": ["right_option"]
                                }
        },
  "to": [
        {
          "key_code": "non_us_backslash",
          "modifiers": "right_option"
                                }

Now, if you want a single-key-combination your "from": could be for example:

"from": { "key_code": "grave_accent_and_tilde" }   -- use any key you like!
    "to": [
        {
          "key_code": "non_us_backslash",
          "modifiers": "right_option"
                                }