Duplicate line for XCode

Readme.txt

sudo subl /Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Versions/A/Resources/IDETextKeyBindingSet.plist

add the following:
<key>Customized</key>
  <dict>
    <key>Duplicate Lines</key>
    <string>selectLine:, copy:, moveToEndOfLine:, insertNewline:, paste:, deleteBackward:</string>
    <key>Duplicate Current Line</key>
    <string>moveToBeginningOfLine:, deleteToEndOfLine:, yank:, insertNewline:, moveToBeginningOfLine:, yank:</string>
</dict>

Go to XCode preferences and search for "Duplicate line" command in key bindings to assign the shortcut. I use Shift-Ctrl-D.