What To Know
- The PARM keyword allows you to specify parameters that override the default settings of a control card.
- Can I override multiple parameters of a control card using the PARM keyword.
- How do I override a DD statement that does not have a name.
In the realm of mainframe computing, JCL (Job Control Language) plays a pivotal role in orchestrating job execution. Control cards, the backbone of JCL, govern various aspects of job processing. However, there may arise situations where you need to override these default settings to achieve specific requirements. This blog post will delve into the intricacies of overriding control cards in JCL, empowering you to customize job behavior with precision.
Understanding Control Cards
Control cards are JCL statements that define job parameters, resource allocation, and execution flow. They typically begin with a unique identifier in columns 1-2, followed by parameters that specify job characteristics. Common control cards include JOB, EXEC, SYSIN, and DD.
Methods for Overriding Control Cards
There are two primary methods for overriding control cards in JCL:
1. Using the PARM Keyword
The PARM keyword allows you to specify parameters that override the default settings of a control card. The syntax is as follows:
“`
CONTROL_CARD_NAME PARM=’OVERRIDE_PARAMETERS’
“`
For example, to override the REGION parameter of the JOB card, you can use:
“`
JOB PARM=’REGION=1024M’
“`
2. Using the DD Override Statement
The DD override statement provides a more granular approach to overriding DD statements. It allows you to specify specific attributes of a DD statement, such as the dataset name, disposition, or access method. The syntax is:
“`
//DD_NAME DD OVERRIDE=(OVERRIDE_ATTRIBUTES)
“`
For example, to override the DISP parameter of the DD statement named INPUT, you can use:
“`
//INPUT DD OVERRIDE=(DISP=KEEP)
“`
Overriding Control Card Examples
To illustrate the practical application of control card overriding, let’s explore a few examples:
1. Overriding the Job Name
“`
//JOBNAME JOB (NEW_JOB_NAME),REGION=1024M
“`
2. Overriding the Execution Parameters
“`
//STEP1 EXEC PGM=MY_PROGRAM,PARM=’OPTION1=VALUE1,OPTION2=VALUE2′
“`
3. Overriding DD Statement Attributes
“`
//MY_DATASET DD OVERRIDE=(DSN=NEW_DATASET_NAME,DISP=KEEP)
“`
Considerations and Best Practices
When overriding control cards, consider the following best practices:
- Limit overrides to specific parameters or DD statements to maintain clarity and avoid conflicts.
- Use the PARM keyword for general overrides and the DD override statement for more granular control.
- Thoroughly test any overrides before production use to ensure expected behavior.
- Document all overrides clearly for future maintenance.
Summary: Unleashing the Power of Customization
Overriding control cards in JCL empowers you to tailor job execution to meet specific requirements. By leveraging the PARM keyword and DD override statement, you can customize job parameters, resource allocation, and data handling with precision. Embrace the art of control card overriding to unlock the full potential of JCL and streamline your mainframe operations.
Quick Answers to Your FAQs
Q: Can I override multiple parameters of a control card using the PARM keyword?
A: Yes, you can specify multiple parameters separated by commas within the PARM keyword.
Q: How do I override a DD statement that does not have a name?
A: Use the default DD statement name of DD* to override unnamed DD statements.
Q: Is it possible to override the JCL procedure name?
A: Yes, you can override the procedure name using the EXEC PGM=PROC statement.
