VMS Help System Services, $SETDDIR, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 new-dir-addr

    OpenVMS usage:char_string
    type:         character-coded text string
    access:       read only
    mechanism:    by descriptor-fixed-length string descriptor
    A descriptor of the new default directory. The new-dir-addr
    argument is the address of the descriptor that points to the
    buffer containing the new directory specification that RMS will
    use to set the new process-default directory. If the default
    directory is not to be changed, the value of the new-dir-addr
    argument should be 0.

 length-addr

    OpenVMS usage:word_unsigned
    type:         word (unsigned)
    access:       write only
    mechanism:    by reference
    A word that is to receive the length of the current default
    directory. The length-addr argument is the address of the word
    that will receive the length. If you do not want this value
    returned, specify the value 0.

 cur-dir-addr

    OpenVMS usage:char_string
    type:         character-coded text string
    access:       write only
    mechanism:    by descriptor-fixed-length string descriptor
    A descriptor of a buffer that is to receive the current default
    directory string. The cur-dir-addr argument is the address of the
    descriptor that points to the buffer area that is to receive the
    current directory string.