/CONFIRM
       /NOCONFIRM (default)

    Controls whether the STARTUP MODIFY command displays the
    file specification of each file before modifying its startup
    characteristics in the startup data file and requests you to
    confirm that the file characteristics be modified. If you specify
    /CONFIRM, you must respond to the prompt with a Y (Yes) or a
    T (True) and press Return before the file is modified. If you
    enter anything else, such as N or No, the requested file is not
    modified.