Changing modifier keys from the command line

Question

As a heavy Emacs user, I like to remap my Caps Lock key to function as the Ctrl key. There is a convenient dialog in the Keyboard Preference Pane to do that. But the problem is that this setting gets lost after someone logs into another account that hasn't this preference set.

So is there any way of doing the same as the preference pane dialog from the command line?

Answer 1

Changing preferences and running, defaults -currentHost read -g shows you what changes are being written. I was going to write up a short bash script to automate it, but it looks like I was beaten to the punch:

#!/bin/bash                                                                      

mappingplist=com.apple.keyboard.modifiermapping

if [ $1 == "emacs" ]; then
    echo "Switching to emacs modifiers"
    defaults -currentHost write -g $mappingplist '(                              
                {                                                                
            HIDKeyboardModifierMappingDst = 4;                                   
            HIDKeyboardModifierMappingSrc = 2; },                                
                {                                                                
            HIDKeyboardModifierMappingDst = 12;                                  
            HIDKeyboardModifierMappingSrc = 10;                                  
        },                                                                       
                {                                                                
            HIDKeyboardModifierMappingDst = 2;                                   
            HIDKeyboardModifierMappingSrc = 4;                                   
        },                                                                       
                {                                                                
            HIDKeyboardModifierMappingDst = 10;                                  
            HIDKeyboardModifierMappingSrc = 12;                                  
        })'


else
    echo "Switching to default modifiers"
    defaults -currentHost delete -g $mappingplist
fi

The script takes one argument, if the argument is emacs, then it swaps command and control, if the argument is anything else it restores the defaults.

http://forums.macrumors.com/showthread.php?t=949280

Answer 2

You can use KeyRemap4MacBook with the PCKeyBoardHack. It also allows you to use Emacs keys in any Mac app, including the ones not using Cocoa such as MS apps.

Answer 3

From "Updating modifier key mappings through defaults command tool":

defaults -currentHost write -g com.apple.keyboard.modifiermapping.1133-50475-0 -array '<dict><key>HIDKeyboardModifierMappingSrc</key><integer>0</integer><key>HIDKeyboardModifierMappingDst</key><integer>2</integer></dict>

Change 1133 and 50475 to the vendor and product IDs shown by ioreg -n IOHIDKeyboard -r. src 0 and dst -1 would disable caps lock.

defaults -currentHost write -g modifies:

~/Library/Preferences/ByHost/.GlobalPreferences.*.plist

You have to log out and back in to apply changes. If the values are strings (like in the answer by @pithyless), the changes are shown in System Preferences but they don't have any effect.

Values of keys:

-1 none
0 caps lock
1 left shift
2 left control
3 left option
4 left command
5 keypad 0
6 help
9 right shift
10 right control
11 right option
12 right command

Answer 4

I wanted to swap Right Command with Right Option keys only.

When I setup global Command and Option swap in System Preferences... > Keyboard > Modifier Keys..., there is following config in the system (which works as expected):

$ defaults -currentHost read -g com.apple.keyboard.modifiermapping.1452-591-0
(
        {
        HIDKeyboardModifierMappingDst = 30064771299;
        HIDKeyboardModifierMappingSrc = 30064771298;
    },
        {
        HIDKeyboardModifierMappingDst = 30064771303;
        HIDKeyboardModifierMappingSrc = 30064771302;
    },
        {
        HIDKeyboardModifierMappingDst = 30064771298;
        HIDKeyboardModifierMappingSrc = 30064771299;
    },
        {
        HIDKeyboardModifierMappingDst = 30064771302;
        HIDKeyboardModifierMappingSrc = 30064771303;
    }
)

But when I modify it, to swap only Right side as below - it doesn't work:

$ defaults -currentHost write -g com.apple.keyboard.modifiermapping.1452-591-0 '(
        {
        HIDKeyboardModifierMappingDst = 30064771303;
        HIDKeyboardModifierMappingSrc = 30064771302;
    },
        {
        HIDKeyboardModifierMappingDst = 30064771302;
        HIDKeyboardModifierMappingSrc = 30064771303;
    }
)'

It's because values are written as strings not integers. You can see that using:

$ plutil -convert xml1 -o - ~/Library/Preferences/ByHost/.GlobalPreferences.*.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>com.apple.keyboard.modifiermapping.1452-591-0</key>
    <array>
        <dict>
            <key>HIDKeyboardModifierMappingDst</key>
            <string>30064771303</string>
            <key>HIDKeyboardModifierMappingSrc</key>
            <string>30064771302</string>
        </dict>
        <dict>
            <key>HIDKeyboardModifierMappingDst</key>
            <string>30064771302</string>
            <key>HIDKeyboardModifierMappingSrc</key>
            <string>30064771303</string>
        </dict>
    </array>
</dict>
</plist>

So the right way to update the setting is using XML format:

$ defaults -currentHost write -g com.apple.keyboard.modifiermapping.1452-591-0 -array \
'<dict>
    <key>HIDKeyboardModifierMappingDst</key>
    <integer>30064771303</integer>
    <key>HIDKeyboardModifierMappingSrc</key>
    <integer>30064771302</integer>
</dict>' \
'<dict>
    <key>HIDKeyboardModifierMappingDst</key>
    <integer>30064771302</integer>
    <key>HIDKeyboardModifierMappingSrc</key>
    <integer>30064771303</integer>
</dict>'

At the end, you have to log off and log in again.

Answer 5

Combining a few answers together I came up with this script that seems to work (mapping Caps-lock to Control).

$ keyboard_id = "$(ioreg -n IOHIDKeyboard -r | grep -e VendorID\" -e ProductID | tr -d \"\|[:blank:] | cut -d\= -f2 | tr '\n' -)"
$ defaults -currentHost write -g "com.apple.keyboard.modifiermapping.${keyboard_id}0" '(
{
  HIDKeyboardModifierMappingDst = 2;
  HIDKeyboardModifierMappingSrc = 0;
})'

Only problem that it doesn't seem to take any effect... :(

I'll update if it I get it to work.