18.4 Environments

The system under which REXX procedures run is assumed to include at least one environment for processing commands. An environment is selected by default on entry to a REXX procedure.

You can change the environment by using the ADDRESS instruction:

address

cms

/*

VM/ESA CMS environment */

address

POWER

/*

VSE/ESA POWER host command environment */

address TSO ²ALLOC F(SYSOUT) DSN(my.dsn) SHR² address DOS ¢ DIR MDV1.ALL¢

TSO ISPF dialog invocation:

address ISPEXEC ²SELECT CMD(%myexec) ²

You can find out the name of the current environment by using the ADDRESS built-in function. ADDRESS() returns the name of the environment to which commands are currently being submitted.

if address() = ¢ CMD¢ then /* OS/2 environment

*/

The underlying operating system defines environments external to the REXX procedure.

The environment selected depends on the caller. For example if a procedure is called from CMS, the default environment is CMS. If called from an editor that accepts subcommands from the language processor, the default environment may be that editor.

ADDRESS temporarily or permanently changes the destination of commands. Commands are strings, not interpreted by REXX itself but sent to an external environment.

18.4.1 VSE/ESA Environment

REXX/VSE provides the following host command environments:

VSE for the REXX/VSE commands.

POWER for VSE/POWER spool-access service requests. JCL to issue JCL commands via a REXX program. CONSOLE lets you manage console sessions.

LINK and LINKPGM for linking to a program.

18.4.2 VM/ESA Environment

VM/ESA provides among others the following host command environments:

CMS implies full command resolution just as provided in usual interactive command (terminal) mode.

COMMAND implies basic CMS CMSCALL command resolution.

CPICOMM can be used to call program-to-program communications routines. OPENVM can be used to call OPENVM-type CSL routines, such as OpenEdition for VM/ESA callable services.

370VSE to OS/390 Migration Workbook

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IBM OS/390 manual Environments, 18.4.1 VSE/ESA Environment, 18.4.2 VM/ESA Environment, Power

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.