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OPEN DATASET - os_additions

Quick Reference

Other versions: 7.31 | 7.40 | 7.54

Syntax


... [TYPE attr] 
    [FILTER opcom] ...

Extras

1. ... TYPE attr
2. ... FILTER opcom

Effect

These additions can be used to make operating system-specific settings and set operating system statements.

Addition 1

... TYPE attr

Effect

The behavior of this addition is determined by the operating system of the host computer server of the current AS Instance. If the operating system is not an MS Windows operating system, a character-like field can be specified for attr that contains operating system-specific parameters for the file that is to be opened. These parameters are passed to the operating system of the AS Instance unchanged, and without being checked for correctness.

If the operating system is an MS Windows operating system, and the file is opened as a text file or as a legacy text file and the addition WITH LINEFEED is not used, the content of attr controls the end-of-line marking of the text file:

  • If attr contains the value "NT", the end-of-line is marked by "CRLF".

  • If attr contains the value "UNIX", the end-of-line is marked by "LF".

    • All other values of attr are ignored in MS Windows operating systems, and the end-of-line marking is opened in the same way as described in the addition WITH LINEFEED.


    Note

    Instead of specifying the values "UNIX" or "NT" after TYPE, it is best to use the addition WITH LINEFEED. If it is used, the values "UNIX" or "NT" cannot be specified.


    Example

    Creating a file test.dat. The properties entered under TYPE are specific for the operating system IBM i5/OS (previously OS/400).

    OPEN DATASET 'test.dat' 
  TYPE 'lrecl=80, blksize=8000, recfm=FB' 
  FOR OUTPUT IN TEXT MODE 
             ENCODING DEFAULT 
             WITH SMART LINEFEED.

    Addition 2

    ... FILTER opcom

    Effect

    This addition can be used if the operating system of the current AS Instance host computer supports pipes (Unix and MS Windows). A character-like field can be specified for opcom, which contains an operating system statement that corresponds to the appropriate command-level syntax.

    When the statement OPEN DATASET is executed, a process is started in the operating system for the specified statement. When the file is opened for reading, a channel (pipe) is linked with STDOUT of the process, from which the data is read during file reading. The file itself is linked with STDIN of the process. When the file is opened for writing, a channel (pipe) is linked to STDIN of the process, to which data is passed when writing. The output of the process is diverted to this file.

    If, as part of the automatic authorization check for file access, the database table SPTH is used to make a check using the authorization group and the authorization object S_PATH, the current user must have an authorization for the activity "A6" (Read) or "A7" (Change) when using the addition FILTER.

    The addition FILTER must not be used together with the addition AT POSITION or for the access type FOR UPDATE.


    Notes

    • When working with pipes, it must be ensured that the pipe only exists in the current work process. If the work process is switched while the file is open, the pipe is lost and any attempted reads or writes raise a handleable exception of the class CX_SY_PIPE_REOPEN.
    • Pipes should only be used for operating system statements required in association with files. No other operating system statements should be used. Use the SXPG framework instead. See also Unwanted Calls of Operating System Statements.
    • When the authorization object S_PATH is checked, for compatibility reasons an empty value is also accepted for the activity alongside the values "A6" or "A7" if the addition FILTER is used.

    Security Note

    Using operating system statements that are injected into a program from outside is a serious security risk. Any statements passed to a program from outside must be checked thoroughly before being used. See System Command Injections.


    Example

    On a Unix platform, the statement gzip is used as a write filter and the statement gzip -d is used as a read filter. When the file is accessed for writing the data is compressed, and when it is accessed for reading, the data is decompressed.

    DATA file TYPE string VALUE `/usr/test.Z`. 

OPEN DATASET file FOR OUTPUT IN BINARY MODE 
                      FILTER 'gzip'. 
... 
CLOSE DATASET file. 

OPEN DATASET file FOR INPUT IN BINARY MODE 
                     FILTER 'gzip -d'. 
... 
CLOSE DATASET file.