string
    Specifies the new prompt string. The following rules apply:
    o  All valid ASCII characters can be used.
    o  No more than 64 characters are allowed.
    o  To include spaces or lowercase letters, enclose the string
       in quotation marks (" ").  Otherwise, letters are converted
       automatically to uppercase; leading and trailing spaces are
       removed.
    If you do not specify the string parameter with the SET PROMPT
    command, the default DCL prompt ($  ) is restored.