How to read a VSAM file sequentially from first to last entry or vice versa

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Issue/Introduction

It may be necessary to read a complete file sequentially from the first to the last entry or vice versa.

Here you find an example of doing this with low effort using NCL.

Resolution

NCL provides access to VSAM-Clusters by using &FILE verbs.

It may be necessary to read a complete file sequentially from the first to the last entry or vice versa. An easy way to get the first (or the last) entry of a File is by using parameter OPT=FWD (or OPT=BWD) in the first &FILE GET statement. The key of that &FILE GET is stored in &FILEKEY. In the loop you read the next entry by using OPT=FWD (or OPT=BWD) again without referencing a key value! The loop is controlled by the Feedback provided into variable &FILEKEY. As long as this value is 0, a record from the file could be read. When trying to read after the last record was read, &FILEKEY contains 4 and the loop ends.

Note: You will only get the first record of a file using OPT=FWD if there was no prior &FILE GET to that file.

The following example shows how a complete file is read in ascending order. The fields of the file are read into variables &1, &2, etc as ARGS is used:

========================================================================================
-*---------------------------------------*
-* Reading a file in ascending order     *
-*---------------------------------------*
&FILE GET DD=<ddname> OPT=FWD ARGS
&DOWHILE &FILERC = 0
  ...
  processing of read record
  ...
  &FILE GET DD=<ddname> OPT=FWD ARGS
&DOEND
 ========================================================================================

The complete file can be read in descending order, too. Two small changes in the above example will fulfill that:

• Change OPT=FWD to OPT=BWD in both &FILE GET statements:

========================================================================================
-*---------------------------------------*
-* Reading a file in descending order    *
-*---------------------------------------*
&FILE GET DD=<ddname> OPT=BWD ARGS
&DOWHILE &FILERC = 0
  ...
  processing of read record
  ...
  &FILE GET DD=<ddname> OPT=BWD ARGS
&DOEND
========================================================================================