Twoftpd back-end switcher.
twoftpd-switch
twoftpd-switch examines the value of $SHELL to determine which back-end to execute. If $SHELL_WRITEONLY is set and matches the value of $SHELL, twoftpd-drop is executed. If $SHELL_READONLY is set and matches the value of $SHELL, twoftpd-anon is executed. Otherwise, twoftpd-xfer is executed.
twoftpd-switch prefixes the commands with the path in which the programs were installed.