anchor.diff:                           "shell. (E.g. --apps app1,app2,app3) Defaults "
                            "to rebar.config {shell, [{apps, Apps}]} or "
                            "relx apps if not specified."},
  +                        {start_clean, undefined, "start-clean", boolean,
  +                         "Cancel any applications in the 'apps' list "
  +                         "or release."},
                           {user_drv_args, undefined, "user_drv_args", string,
                            "Arguments passed to user_drv start function for "
                            "creating custom shells."}]}
  
positive.code:     {Opts, _} = rebar_state:command_parsed_args(State),
      case debug_get_value(apps, Opts, no_value,
                           "Found shell apps from command line option.") of
          no_value -> no_value;
          AppsStr ->
              [ list_to_atom(AppStr)
                || AppStr <- rebar_string:lexemes(AppsStr, " ,:") ]
  
negative.code:             ?DEBUG("No script_file specified.", []),
              ok;
          "none" ->
              ?DEBUG("Shell script execution skipped (--script none).", []),
              ok;
          RelFile ->
              File = filename:absname(RelFile),
  