VMS Help OPEN, Qualifiers  *Conan The Librarian (sorry for the slow response - running on an old VAX)

1 - /APPEND

    Opens an existing file for writing and positions the record
    pointer at the end-of-file (EOF). New records are added to the
    end of the file.

    Only sequential files allow more than one user to append records
    concurrently.

    Use the /APPEND qualifier only to add records to an existing
    file. The /APPEND and the /WRITE qualifiers are mutually
    exclusive.

2 - /ERROR

       /ERROR=label

    Transfers control to the location specified by the label keyword
    (in a command procedure) if the open operation results in an
    error. The error routine specified for this qualifier overrides
    any ON condition action specified. If the /ERROR qualifier is not
    specified, the current ON condition action is taken.

    If an error occurs and the target label is successfully given
    control, the global symbol $STATUS retains the code for the error
    that caused the error path to be taken.

3 - /READ

       /READ (default)

    Opens the file for reading. If you specify the /READ qualifier
    without the /WRITE qualifier, you must specify an existing file.

4 - /SHARE

       /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.

5 - /WRITE

    Opens the file for writing. The following restrictions apply to
    the /WRITE qualifier:

    o  Use the /WRITE qualifier to open and create a new, sequential
       file. If the file specification on an OPEN/WRITE command does
       not include a file version number, and if a file with the
       specified file name and file type already exists, a new file
       with a version number one greater than the existing file is
       created.

    o  Use the /READ qualifier with the /WRITE qualifier to open
       an existing file. When the file is opened, the pointer is
       positioned to the beginning of the file. (This differs from
       OPEN/APPEND, which positions the pointer at the end of the
       file.) You cannot use OPEN/READ/WRITE to create a new file.

    o  The /WRITE and the /APPEND qualifiers are mutually exclusive.