Mimic PC NumLock on Mac with 101/102 Key PC Keyboard

I use a MacBook Pro with a leftover Dell 102-key PC keyboard. For almost everything it works great. Even the volume keys work. However, the NumLock doesn't behave the way it does on a PC.

I mostly use the number pad on the right to move the cursor around for editing. It makes editing really fast because the cursor keys are easily reached; just like using the A,S,D,W keys for navigating in a video game. I rarely use the number pad for entering numbers; just when I have a long series of number I want to rapidly input. If it's only one or two numbers, I use the number keys at the top of the keyboard. Using the NumLock key to switch back and forth between cursor control and number entry is extremely handy, but the Apple keyboard doesn't have this feature.

Karabiner to the rescue

I found a popular keyboard-mapping utility for Mac called Karabiner. It allows me to remap the keyboard for specific keyboards, so I can map the keypad 0-9 keys to cursor movement for just the Dell keyboard; however I can't quickly switch back to the default functions.

Map NumLock to toggle between keyboard profiles

The solution is to create 2 keyboard profiles. I modified the "Default profile" to map the keypad keys for cursor movement and created another profile, "NumLock On" that reverts to the original function of the keypad keys for number entry. Then I mapped the NumLock key to run a shell_command calling Karabiner from the command line and loading the other profile. You can see the way it's set up in ~/.config/karabiner/karabiner.json. Here is the relevant code:

    {   
        "from": {
            "key_code": "keypad_9"
        },
        "to": {
            "key_code": "page_up"
        }
    },
    {
        "from": {
            "key_code": "keypad_num_lock"
        },
        "to": {
            "shell_command": "'/Library/Application Support/org.pqrs/Karabiner-Elements/bin/karabiner_cli' --select-profile 'NumLock On'"
        }
    },
    {
        "from": {
            "key_code": "keypad_period"
        },
        "to": {
            "key_code": "delete_forward"
        }
    }

The key_code, "keypad_num_lock", in the profile, "Default profile", is mapped to a "shell_command" which runs the Karabiner command-line interface (cli) and selects the "NumLock On" profile.

In the "NumLock On" profile, keypad_num_lock also runs the Karabiner cli but selects the "Default profile", like this:

     {
         "from": {
             "key_code": "f12"
         },
         "to": {
             "consumer_key_code": "volume_increment"
         }
     },
     {
         "from": {
             "key_code": "keypad_num_lock"
         },
         "to": {
             "shell_command": "'/Library/Application Support/org.pqrs/Karabiner-Elements/bin/karabiner_cli' --select-profile 'Default profile'"
         }
     }

For more on Karabiner, see:

Karabiner Manual

Karabiner JSON Reference Manual