Remapping keys on macOS

2020-06-24T08:00:00+08:00

I ramble a bit here - you may want to skip to how to remap keys on macOS</a>.

I attended WWDC</a> for the first time ever (making lemonade in the COVID-19 situation), and after watching the keynote</a>, got pretty excited about macOS Big Sur.

I wanted to install the macOS Big Sur developer beta but not at the expense of making my main development MacBook Pro virtually unusable. One of the things I thought I really needed working was Karabiner-Elements</a>, which I use to remap keys, specifically:

Caps Lock</code> to Esc</code></li>
Esc</code> to `</code></li> </ul>This particular remapping is really because I use `</code> (backtick) as my tmux</a> prefix key. I picked this up from an ex-colleague</a> after watching him fly while switching tmux panes. And I use either a compact 60% or 65% keyboard which meant I didn't have a dedicated `</code> key - I'd have to hit Fn-Esc</code> which is even more terrible than the default of Ctrl-B</code>. Unsurprisingly, Karabiner-Elements was not working in Big Sur</a>. Not satisfied with that, I quickly found that macOS has supported native key remapping</a> since macOS Sierra via the hidutil</code> command-line tool. If you're not beyond scrappily writing some JSON and XML, this just works: Decide what keys you want to remap. In my case, I wanted to remap Caps Lock</code> to Esc</code>.</li> Apple's docs</a> say: The keys take a hexadecimal value that consists of 0x700000000 or’d with the desired keyboard usage value</blockquote> Pretty cryptic, but what it really means is you just have to add 0x700000000</code> to your key's "usage ID" in this table</a> (techically, this is a bitwise OR</code>, which is not addition, but the usage IDs are small enough for it to not matter). </li> Caps Lock</code>'s usage ID is 0x39</code>. Adding 0x700000000</code> to that gives 0x700000039</code>. </li> Esc</code>'s usage ID is 0x29</code> - we'll use 0x700000029</code>.</li> Caps Lock</code> (0x700000039</code>) is the source, so we will specify "HIDKeyboardModifierMappingSrc": 0x700000039</code>.</li> Esc</code> (0x700000029</code>) is the destination, so we will specify "HIDKeyboardModifierMappingDst": 0x700000029</code>.</li> Repeat for each pair of keys you want to remap.</li> Try it out in the command-line: hidutil property --set '{"UserKeyMapping":[ { "HIDKeyboardModifierMappingSrc": 0x700000039, "HIDKeyboardModifierMappingDst": 0x700000029 }, { "HIDKeyboardModifierMappingSrc": 0x700000029, "HIDKeyboardModifierMappingDst": 0x700000035 } ]}'</pre> </li> This remapping will be undone whenever you reboot your Mac, so one way to persist the remapping is to run the hidutil</code> command every time your Mac boots. For that, we can rely on Launch Agents</a>. Create a file named ~/Library/LaunchAgents/com.example.KeyRemapping.plist</code>:

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Remapping keys on macOS