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.