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BYPASS

Enhanced Definition

Key Characteristics

- Conditional Execution: Bypassing is almost always conditional, based on specific criteria such as return codes, input parameters, or data values.
- Controlled Alteration: It represents a deliberate and controlled deviation from the default or intended processing path, not an accidental error or system failure.
- Implementation Methods: Can be achieved through JCL parameters (e.g., COND, IF/THEN/ELSE), utility control statements (e.g., SKIP in sort utilities), or explicit logic within application programs (e.g., IF statements in COBOL).
- Temporary or Permanent: Bypasses can be temporary (e.g., during a specific test run or for a one-time fix) or more permanent (e.g., a long-standing conditional logic in a production job or program).
- Impact on Data Flow: Skipping a step can have significant implications for subsequent steps, potentially affecting data integrity, the availability of expected output, or the overall success of a batch process.

Use Cases

- JCL Step Skipping: Using the COND parameter in JCL to prevent a job step from executing if a previous step failed or met a specific return code.
```
jcl
//STEP02 EXEC PGM=ANOTHERPGM,COND=(8,LT,STEP01)
```
This step will bypass if STEP01's return code is 8 or greater.
- Programmatic Record Skipping: A COBOL program might BYPASS processing a specific record type in an input file based on a flag or a data value within the record itself, e.g., skipping header or trailer records.
```
cobol
IF RECORD-TYPE = 'HEADER' OR 'TRAILER'
PERFORM READ-NEXT-RECORD
ELSE
PERFORM PROCESS-DETAIL-RECORD.
```
- Utility Function Bypass: Using control statements in utilities like DFSORT or IDCAMS to skip certain records, steps, or functions (e.g., SKIPREC in DFSORT to bypass initial records in a file).
- Error Recovery: Temporarily bypassing a problematic job step or program module to allow other parts of a critical batch run to complete while the issue is being investigated.
- Maintenance or Testing: Bypassing a production update step during a test run to validate other parts of the job without affecting live data, or to skip non-essential steps during system maintenance.

Related Concepts

Bypassing is closely related to conditional processing and error handling. JCL's COND parameter and IF/THEN/ELSE/ENDIF constructs are primary mechanisms for implementing bypass logic at the job step level, allowing steps to be skipped based on return codes from prior steps. Within application programs, IF statements and control flow logic enable programmatic bypasses of code sections or data records, often as part of robust exception handling or data validation. It also ties into job control and workflow management, as it allows for dynamic adjustment of execution paths based on runtime conditions, enhancing the flexibility and resilience of batch processes.

Best Practices:

Document Thoroughly: Any bypass logic, especially in production JCL or programs, must be clearly documented, explaining the reason, conditions, and expected outcome.
Minimize Unnecessary Bypasses: Avoid introducing bypasses unless absolutely necessary, as they can complicate debugging, maintenance,

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