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

       /SHARE[=option]

    Opens the specified file as a shareable file to allow other users
    read or write access. If you specify the /SHARE=READ qualifier,
    other users are allowed read (R) access to the file, but not
    write (W) access. If you specify the /SHARE=WRITE or the /SHARE
    qualifier with no option, users are allowed read and write access
    to the specified file.

    If the /SHARE qualifier is not present, other users are allowed
    only read access to the specified file.