IBM OS/390 manual Spooling, JCL Differences Between VSE and MVS, Job Input

4.2.1.7 Instream Data

Both operating systems allow Instream Data in the middle of the JCL. This is data that will be processed by the executing program.

4.2.1.8 Variables

The JCL in both operating systems will accept variables. These variables are set with the // SET statement in MVS, or SETPARM in VSE.

4.2.1.9 Conditional JCL

Conditional JCL exists in both environments and allows performing IF and GOTO statements. Loops are prohibited. In MVS, the IF statements are all processed at converter time. Although the mechanics are very different, functionally, the IFs are the same in both environments.

4.2.1.10 Return Codes

Return codes from previous steps can also be tested during execution in both environments. Program steps can be bypassed based on the result of testing for a condition (a return code or a parameter value). For example, if in a statement, the return code was more than zero, then bypass the next statement. In MVS, this is handled by the COND parameter on the // EXEC statement.

See also 4.3.11.3, ªMVS Conditional JCLº on page 84.

4.2.2 Spooling

Spooling exists in both environments. POWER for VSE and JES for OS/390. POWER and JES provide similar input and output capabilities and a similar system of classes and priorities.

4.2.2.1 Internal Reader

The internal reader facility exists in both environments. An application program can pass jobs to the spool, right into the input queue, just by writing to a pseudo punch device. RJE and NJE also exist in both environments.

Further discussion of spooling can be found in Chapter 10, ªPOWER and JES2º on page 207.

4.3 JCL Differences Between VSE and MVS

In part because of the differences in philosophy discussed in 4.1, ªThe Philosophy of JCL in System/390º on page 69, there are differences in the processing of JCL that lead to Job Control Language differences between the two environments.

4.3.1 Job Input

In VSE systems, job input consisting of JCL statements and instream data, whether spooled through the POWER spooling system or directly read in a partition, is processed in a strictly sequential process. That is, a program can only read one input statement at any one time, and this is a sequential process. A programming or JCL error in VSE can cause the VSE Job Control program to read a user data statement, or a user program to read a JCL statement, with unpredictable results.

Chapter 4. Job Control Language (JCL) Differences and Considerations 73