Opens a file for reading, writing, or both; assigns a logical
    name to a file; and places the name in the process logical name
    table.

    See the qualifier descriptions for restrictions.

    Format

      OPEN  logical-name[:] filespec

1  –  Parameters

 logical-name[:]

    Specifies the logical name and a character string to be assigned
    to the file.

 filespec

    Specifies the name of the file or device being opened for input
    or output. The file type defaults to DAT. The asterisk (*)  and
    the percent sign (%)  wildcard characters are not allowed.

    To create a new, sequential file, specify the /WRITE qualifier.
    See the description of the /WRITE qualifier for more information.

2  –  Qualifiers

2.1    /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.

2.2    /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.

2.3    /READ

       /READ (default)

    Opens the file for reading. If you open a file with /READ, other
    users are also allowed read access to the file, but no user is
    allowed write access. If you open a file with /READ/WRITE, no
    other users are allowed access while the file is open. If you
    specify the /READ qualifier without the /WRITE qualifier, you
    must specify an existing file.

2.4    /SHARE

       /SHARE[=option]
       /NOSHARE (Alpha/Integrity servers only)

    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.

    To open a file with no shared access, specify /NOSHARE or use
    OPEN/READ/WRITE.

2.5    /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. While the file is open, no other user will have
       access to it. When the file is first 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.

3  –  Examples

    1.$ OPEN INPUT_FILE AVERAGE.DAT
      $ READ_LOOP:
      $ READ/END_OF_FILE=ENDIT  INPUT_FILE  NUM
         .
         .
         .
      $ GOTO READ_LOOP
      $ ENDIT:
      $ CLOSE INPUT_FILE

      The OPEN command opens the file named AVERAGE.DAT as an input
      file and assigns it the logical name INPUT_FILE. The file is
      opened with read access because the /READ qualifier is present
      by default. The READ command reads a record from the logical
      file INPUT_FILE into the symbol named NUM. The procedure
      executes the lines between the labels READ_LOOP and ENDIT until
      the end of the file is reached. At the end of the file, the
      CLOSE command closes the file.

    2.$ OPEN/WRITE/ERROR=OPEN_ERROR  OUTPUT_FILE  TEMP.OUT
      $ COUNT = 0
      $ WRITE_LOOP:
      $ COUNT = COUNT + 1
      $ IF COUNT .EQ. 11 THEN GOTO ENDIT
      $ WRITE OUTPUT_FILE "Count is ''COUNT'."
         .
         .
         .
      $ GOTO WRITE_LOOP
      $ ENDIT:
      $ CLOSE OUTPUT_FILE
      $ EXIT
      $
      $ OPEN_ERROR:
      $ WRITE SYS$OUTPUT "Cannot open file TEMP.OUT"
      $ EXIT

      The OPEN command with the /WRITE qualifier creates the file
      TEMP.OUT and assigns it the logical name OUTPUT_FILE. TEMP.OUT
      is a sequential file.

      The /ERROR qualifier specifies that if any error occurs while
      opening the file, the command interpreter should transfer
      control to the line at the label OPEN_ERROR. The command
      procedure writes records to the file TEMP.OUT until the symbol
      COUNT equals 11.

    3.$ OPEN/READ INPUT_FILE TRNTO::DKA0:[COST]INVENTORY.DAT
      $ READ_LOOP:
      $ READ/END_OF_FILE=ENDIT  INPUT_FILE  NUM
      $ FIRST_CHAR = F$EXTRACT(0,1,NUM)
      $ WRITE SYS$OUTPUT FIRST_CHAR
      $ GOTO READ_LOOP
      $ ENDIT:
      $ CLOSE INPUT_FILE

      This command procedure opens the file INVENTORY.DAT located at
      remote node TRNTO as an input file, and assigns it the logical
      name INPUT_FILE. The READ command reads a record from the
      logical file INPUT_FILE into the symbol named NUM. The next
      two commands extract the first character from the record and
      write the character to the SYS$OUTPUT device. These two steps
      occur for all records in the file until the procedure reaches
      the end-of-file (EOF). At this point, the CLOSE command closes
      the file and deassigns the logical name INPUT_FILE.