edit file "/Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Resources"
add
<key>Custom ShortCut</key> <dict> <key>Duplicate Line</key> <string>selectLine:, copy:, moveToEndOfLine:, insertNewline:, paste:, deleteBackward:</string> <key>Cut Line</key> <string>selectLine:, copy:, moveToEndOfLine:, deleteToBeginningOfLine:, deleteBackward:</string> </dict>
原文：http://www.cnblogs.com/zemliu/p/4196975.html