 |
JCL Backward References. |
JCL REFERBACK statement or Backwards Reference in JCL is a technique to copy attributes from previous DD statements. You're not required to code these parameters again and again. Instead, all required parameters on the first step and clone attributed in next steps via JCL REFER BACK statements.
Agenda.
- Introduction to Backwards Reference.
- JCL Backward Reference Advantage.
- JCL Backward Reference Syntax.
- JCL Backward References Examples.
Backward Reference Introduction.
A mainframe JCL is a combination of three different job control statements. These job control statements are JOB, DD, and EXEC statements. For each statement, you need to specify many different parameters.
Being a program it is always tough to remember all these parameters. JCL has a facility called "JCL REFERBACK" to clone parameter information from the previous step.
In laymen's terms, JCL REFER BACK is a reference to a previous statement parameter. Backward reference in the JCL can be used in the job or in-stream procedure, or in a cataloged.
JCL Refer back statements are best suited in situations, where you have tons of datasets in a JCL. Now, let's look at the advantage of JCL refer back.
Backward Reference Advantage.
- JCL REFER BACK statement saves time and reduces the possibility of typo error.
- JCL REFER BACK statement is used to clone parameters value from previous steps. It also reduces code change efforts because you need to change the value of the parameter in the first step instead of all steps.
JCL Backward Reference Syntax.
parameter=*.[stepname.]ddname
You can use refer back statements on the following job control statements.
- *.name or *.ddname: It is the referenced statement.
- *.stepname.name or *.stepname.ddname: It is the referenced statement in the jcl.
- *.stepname.procstepname.ddname: It is the proc step name or DDname etc with in the cataloged procedure or instream procedure.
JCL Backword Reference Rules.
You can use JCL backward reference statement to copy previously coded parameters. But, JCL refers back is not applicable for all job control statements. Following are the examples.
- DD DUMMY Statement.
- SYSOUT DD Statement.
- DD * statements in DSN-NAME etc.
Backward References Examples.
Example 1: In the below example, both refer and referenced steps are in the same step.
//TPXPTX01 JOB ..... (JOB CARD Parameters)//CALTAX01 EXEC PGM=TXTP01
//EMPTX DD DSNAME=TP.EMP.INP.FILE . .
//EMPOT DD DSNAME=*.EMPTAX
Example 2: In the below example, both refer and referenced steps are in different steps.
//TPXPTX01 JOB ..... (JOB CARD Parameters)
//CALTAX01 EXEC PGM=TXTP01
//EMPTX DD DSNAME=TP.EMP.INP.FILE . .
//EMPOT DD DSNAME=*.EMPTAX
//*
//CALTAX02 EXEC PGM=TXTP02
//EMPTT DD DSNAME=*.CALTAX01.EMPTAX
Example 3: In the below example, both refer and referenced steps are in cataloged procedures.
Cataloged procedure://EMPSAL EXEC ...//EMPFL DD DSNNAME=TP.PP.SAL.....// .
JCL://TPXPTX01 JOB ..... (JOB CARD Parameters) //CALTAX01 EXEC PROC=EMPTAX01 //EMPTXX DD DSNAME=*.CALTAX01.EMPSAL.EMPFL
Cataloged procedure:
//EMPSAL EXEC ...
//EMPFL DD DSNNAME=TP.PP.SAL.....
// .
JCL:
//EMPTXX DD DSNAME=*.CALTAX01.EMPSAL.EMPFL
JCL Backword Reference Rules.
Conclusion.
Finally, JCL Refer back statement is very important from the programmer's perspective. It not only helps in saving time but also reduces typo mistakes. You can include all relevant parameters in the first step and then used the backward reference technique to copy the same information for all relevant next DD statements in JCL.
► Youtube
► Facebook
► Linkedin
► Reddit
Thank you for your support.
Mainframe Forum™
No comments:
Post a Comment