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CTL - Control

Enhanced Definition

In the mainframe context, "Control" (often abbreviated as `CTL`) refers to **control statements** or **control cards** that provide specific instructions or parameters to a utility program or an application program. These statements dictate how the program should execute, what actions it should perform, or what data it should process, effectively controlling its behavior.

Key Characteristics

- Program-Specific Syntax: Each utility or application program defines its own specific syntax, keywords, and parameters for its control statements, which must be adhered to precisely.
- Input via SYSIN or DD *: Control statements are typically supplied as input to a batch job step, often through a DD statement named SYSIN or directly embedded in the JCL using DD * or DD DATA.
- Directives for Processing: They serve as directives, instructing the program on tasks such as data selection, sorting criteria, file manipulation, report formatting, or specific utility functions.
- Fixed or Variable Format: Depending on the utility or program, control statements can be in a fixed format (requiring specific columns for keywords and values) or a free-form, variable format.
- Critical for Automation: They are fundamental for automating complex batch processes, allowing programs to be highly configurable without requiring code changes.

Use Cases

- IDCAMS Utility: Defining, deleting, or altering VSAM datasets (e.g., DEFINE CLUSTER, DELETE).
```
jcl
//SYSIN    DD *
DEFINE CLUSTER (NAME(MY.VSAM.KSDS) -
VOLUMES(VOL001) -
RECORDS(100 10) -
INDEXED -
KEYS(5 0)) -
DATA (NAME(MY.VSAM.KSDS.DATA)) -
INDEX (NAME(MY.VSAM.KSDS.INDEX))
/*
```
- SORT Utility (DFSORT/SYNCSORT): Specifying sorting, merging, copying, or reporting criteria for datasets.
```
jcl
//SYSIN    DD *
SORT FIELDS=(1,10,CH,A)
OUTREC FIELDS=(1,10,C' ',11,20)
/*
```
- IEBGENER Utility: Copying sequential datasets, often with reformatting, using GENERATE or MEMBER control statements to select specific records or members.
- Application Programs: Providing runtime parameters, configuration settings, or transaction data to custom-written COBOL or Assembler programs, enabling flexible execution.
- Database Utilities (DB2, IMS): Directing database maintenance, reorganization, or backup utilities with specific commands and options to manage database objects.

Related Concepts

Control statements are intrinsically linked to JCL (Job Control Language), as JCL DD statements are used to allocate the dataset (often SYSIN) containing these statements to the executing program. They are the primary mechanism through which batch utilities (like IDCAMS, DFSORT, IEBGENER) receive their operational instructions, making them essential for batch processing. Furthermore, many application programs are designed to read control cards to enable flexible, parameter-driven execution without recompilation, integrating seamlessly into the mainframe