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

       /TRUNCATE (default)
       /NOTRUNCATE

    Controls whether the COPY command truncates an output file at
    the end-of-file (EOF) when copying it. This operation can only be
    used with sequential files.

    By default, the actual size of the input file determines the size
    of the output file. If you select /NOTRUNCATE, the allocation of
    the input file determines the size of the output file.