Ejecución de programa

How to execute a program using JCL?

The JCL, or Job Control Language, is essential for programming in mainframe environments. In this context, you will learn how to run a program with the help of a JCL that you have previously generated. To do this, you start the command window and type top to move to the beginning of the JCL. It is important to know the essential parts of a JOB statement, which include crucial parameters such as the memory to be used and the maximum time of the JOB.

What is included in a JCL?

Throughout the JCL, you will see several important steps that we break down below:

1. JOB statement: always starts with this statement, which defines the usable memory and other parameters.
2. Compilation step: It refers to the procedure or program loaded during the environment configuration:

   //JobJobName JOB ...,// PGM=program_name

3. IFBR14 Utility: Configuration to manage files, allowing to delete and generate new ones:

   IFBR14, ..., DELETE FILE

4. IEBGENER utility: Conditionally backs up files according to the result of previous steps:

   //Use of conditional: IF STEP02 LE 9 THEN

How to add data to an input file?

This is done by accessing the generated files, usually in edit mode. Here you enter data such as the student's name, GPA, and an indicator that determines whether he/she receives a scholarship:

• Scholarship indicator: '1' for scholarship recipient, '0' for non-scholarship recipient.
• Scholarship Amount: fill in all nine digits of this field if on scholarship.

Example entry:

Jose Ganimedes Montes 85 1 0236800Jimena Hernandez Gonzalez 72 0 0000000.

What happens after I submit a JCL?

After you submit(su) the JCL, you will be able to check its execution in the spool. In case of error during execution, it is useful to check the job display console(st repo) to identify problems, such as incorrect spaces in statements.

Common errors:

• Incorrect spaces: Between data and parameter definitions, affect JCL loading.
• Empty input files: Make sure to handle exceptions correctly to avoid critical failures.

How to verify the output of the execution?

The output and correct functioning of your JCL is confirmed in the generated report, where the information is verified:

• Totals read and printed: Of the number of students processed.
• Total amount of scholarships: Only adds up for those indicated as scholarship recipients.

Use this information to check if your JCL is processing the files correctly. Running the JCL with an empty file is a robust practice to check that it will not throw unexpected errors when encountering non-existent data, which must be properly managed.

What should be considered when modifying an existing JCL?

It is common that you need to adjust file names or conditions between runs. Be sure to modify the names and conditions correctly in all steps:

• Updates in files: Modify both the input and output referenced in different steps.
• Proper conditions: When working with different files, keep the conditional logic consistent.

With these techniques and examples, you will continue to expand your skills in using JCL on mainframes, opening up a universe of programming possibilities. I encourage you to continue exploring the world of mainframes, where every session is an opportunity to strengthen your knowledge and skills. Go for more!