VMS Help CMS, DIFFERENCES, file, Qualifiers, /APPEND  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Controls whether CMS appends the command output to an existing
    file, or creates a new file. If you specify /APPEND and the output
    file does not exist, CMS creates a new file. If you do not provide
    an output file specification (see the description for /OUTPUT),
    CMS searches your current default directory for a file with the
    file name specified in the file1 parameter and the file type .DIF.