Add custom commands to Xcode.app and all Xcode-*.app instances, use this every time you update/download a new Xcode.

add_custom_commands_to_xcode

# Add custom commands to Xcode.app and all Xcode-*.app instances.
# Run this every time you update/download Xcode.
function xcodeAddCustomCommands() {
  PLB="/usr/libexec/PlistBuddy"

  # First, update the standard Xcode.app if it exists
  if [[ -d "/Applications/Xcode.app" ]]; then
    echo "Xcode.app found, adding commands"
    PLIST="/Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Versions/Current/Resources/IDETextKeyBindingSet.plist"
    if [[ -f "$PLIST" ]]; then
      # Add the "Duplicate Current Lines Down" command
      $PLB -c "Add :'Custom Commands':'Duplicate Current Lines Down' string 'selectParagraph:, delete:, yank:, moveToBeginningOfParagraph:, yank:, moveUp:, moveToEndOfParagraph:, moveToEndOfLine:'" "$PLIST"
      # Assign Command+D
      $PLB -c "Add :'Custom Commands':'Duplicate Current Lines Down':KeyEquivalent string 'd'" "$PLIST"
      $PLB -c "Add :'Custom Commands':'Duplicate Current Lines Down':ModFlags integer 1048576" "$PLIST"

      # Add the "Delete Current Line" command
      $PLB -c "Add :'Custom Commands':'Delete Current Line' string 'deleteToBeginningOfLine:, moveToEndOfLine:, deleteToBeginningOfLine:, deleteBackward:, moveDown:, moveToEndOfLine:'" "$PLIST"
      # Assign Command+Backspace
      $PLB -c "Add :'Custom Commands':'Delete Current Line':KeyEquivalent string $'\x7F'" "$PLIST"
      $PLB -c "Add :'Custom Commands':'Delete Current Line':ModFlags integer 1048576" "$PLIST"
    fi
  fi

  # Then, update each Xcode-*.app
  for xcodeFolder in /Applications/Xcode-*.app; do
    if [[ -d "$xcodeFolder" ]]; then
      echo "$xcodeFolder found, adding commands"
      PLIST="$xcodeFolder/Contents/Frameworks/IDEKit.framework/Versions/Current/Resources/IDETextKeyBindingSet.plist"
      if [[ -f "$PLIST" ]]; then
        # Add the "Duplicate Current Lines Down" command
        $PLB -c "Add :'Custom Commands':'Duplicate Current Lines Down' string 'selectParagraph:, delete:, yank:, moveToBeginningOfParagraph:, yank:, moveUp:, moveToEndOfParagraph:, moveToEndOfLine:'" "$PLIST"
        # Assign Command+D
        $PLB -c "Add :'Custom Commands':'Duplicate Current Lines Down':KeyEquivalent string 'd'" "$PLIST"
        $PLB -c "Add :'Custom Commands':'Duplicate Current Lines Down':ModFlags integer 1048576" "$PLIST"

        # Add the "Delete Current Line" command
        $PLB -c "Add :'Custom Commands':'Delete Current Line' string 'deleteToBeginningOfLine:, moveToEndOfLine:, deleteToBeginningOfLine:, deleteBackward:, moveDown:, moveToEndOfLine:'" "$PLIST"
        # Assign Command+Backspace
        $PLB -c "Add :'Custom Commands':'Delete Current Line':KeyEquivalent string $'\x7F'" "$PLIST"
        $PLB -c "Add :'Custom Commands':'Delete Current Line':ModFlags integer 1048576" "$PLIST"
      fi
    fi
  done
}