xcode-key-bindings

Since Xcode has to be one of the worst IDE's out there, it comes as no surprise even setting custom key bindings requires some extra work.

Here's how I've done it

1. Open up /Applications/Xcode-Beta.app/Contents/Frameworks/IDEKit.framework/Resources/IDETextKeyBindingSet.plist in a text editor
2. Paste this to the end of the file (or any other custom commands you want)

<key>Custom</key>
<dict>
    <key>Cut Current Line</key>
    <string>selectLine:, copy:, deleteBackward:</string>
    <key>Insert and Move to New Line Below</key>
    <string>moveToEndOfLine:, insertNewline:</string>
    <key>Duplicate Current Line</key>
    <string>moveToBeginningOfLine:, deleteToEndOfLine:, yank:, insertNewline:, moveToBeginningOfLine:, yank:</string>
</dict>

3. Restart Xcode
4. Inside Xcode go to Preferences -> Key Bindings and search for Cut Current Line (or any other key you added previously)
5. Add the desired shortcut (Ctrl X in my case)