I hate that Xcode doesn’t include a duplicate line shortcut. I have to keep adding it in every time a new version of Xcode comes out and every time, I have to Google it, so I’m pasting the SO post here that worked most recently. There must be a better way, but until I figure that out, here’s what has worked for me.
<key>Custom Commands</key> <dict> <key>Cut Current Line</key> <string>selectLine:, cut:</string> <key>Copy Current Line</key> <string>selectLine:, copy:</string> <key>Duplicate Current Line</key> <string>selectLine:, copy:, moveToEndOfLine:, insertNewline:, paste:, deleteBackward:</string> </dict>
Then restart Xcode and go to Preferences -> Key Bindings and assign your shortcuts.
This was taken from: https://stackoverflow.com/a/41579618