/sys$common/syshlp/helplib.hlb DIFFERENCES, Qualifiers, /OUTPUT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /OUTPUT[=filespec]

    Specifies an output file to receive the list of differences.
    By default, the output is written to the current SYS$OUTPUT
    device. If the filespec parameter is not specified, the output
    is directed to the first input file with a file type .DIF. The
    asterisk (*) and the percent sign (%) wildcard characters are not
    allowed.

    When you specify the /OUTPUT qualifier, you can control the
    defaults applied to the output file specification as described
    in the OpenVMS User's Manual. The default output file type is
    .DIF.