prompt

    OpenVMS usage char_string
    type          character string
    access        read only
    mechanism     by reference
    Address of prompt string (zero-terminated ASCII string).

 buffer

    OpenVMS usage char_string
    type          character string
    access        write only
    mechanism     by reference
    Address of buffer to store command.

 buflen

    OpenVMS usage longword_unsigned
    type          longword (unsigned)
    access        read only
    mechanism     by value
    Maximum length of buffer.