CMDLANG - Command Language
CMDLANG, or Command Language, in the z/OS context, primarily refers to the embedded language used within application programs to interact with specific mainframe subsystems, most notably **CICS (Customer Information Control System)**. It provides a standardized way for applications written in host languages like COBOL or PL/I to request services from the subsystem, such as data access, transaction management, and inter-program communication. `CMDLANG` is a crucial parameter used in various IBM mainframe subsystems, such as CICS and DB2, to explicitly specify the programming language of an application program that issues commands or statements to that subsystem. Its primary purpose is to enable the subsystem to correctly interpret the syntax and data structures used by the application, ensuring proper command execution and data exchange.
Key Characteristics
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- Embedded Nature: CMDLANG commands are not standalone; they are embedded directly into the source code of host languages (e.g., COBOL, PL/I, Assembler) and are typically prefixed with
EXEC(e.g.,EXEC CICS,EXEC SQL). - Subsystem Specific: Each mainframe subsystem or product (like CICS, DB2, IMS TM) defines its own set of command language verbs and syntax, tailored to its specific services and functionalities.
- Pre-processed: Before compilation, a dedicated translator or precompiler (e.g., CICS translator, SQL precompiler) processes these embedded commands, converting them into standard host language
CALLstatements or data structures that the host language compiler can understand. - Service Request Mechanism: It serves as the primary API for application programs to request system services, such as reading a file, sending data to a terminal, linking to another program, or performing database operations.
- Standardized Interface: Provides a high-level, consistent interface for developers, abstracting the complexities of the underlying system calls and control blocks.
- Error Handling: Commands typically include mechanisms to return status or response codes (e.g.,
RESPin CICS,SQLCODEin DB2) that indicate the success or failure of the operation, allowing applications to implement robust error handling.
- Embedded Nature: CMDLANG commands are not standalone; they are embedded directly into the source code of host languages (e.g., COBOL, PL/I, Assembler) and are typically prefixed with
Use Cases
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- CICS Transaction Processing: A COBOL program processing an online transaction uses
EXEC CICScommands to interact with 3270 terminals (SEND,RECEIVE), access VSAM files (READ,WRITE), or manage temporary storage (WRITEQ TS). - Database Interaction: Applications use
EXEC SQLcommands (the DB2 Command Language) within COBOL or PL/I programs to query, insert, update, or delete data in DB2 relational databases. - Program Control and Flow: Within CICS,
EXEC CICS LINK PROGRAMis used to transfer control to another program,EXEC CICS RETURNto return control, andEXEC CICS XCTLfor unconditional transfer. - Resource Management: Applications can use CMDLANG to acquire and release system resources, such as dynamic storage (
EXEC CICS GETMAIN) or to control task execution. - Inter-Region Communication: CICS applications can use
EXEC CICS STARTorEXEC CICS LINKwithSYSIDto initiate transactions or link to programs in other CICS regions or even other CICSplexes.
- CICS Transaction Processing: A COBOL program processing an online transaction uses