Developing Applications for Use with UNIX System Services OS/390

Introduction

UNIX System Services (USS) OS/390 provides all the traditional services of the OS/390 operating system plus many new services. Two prominent features of these new services are the USS hierarchical file system (HFS) and the MVS/ESA USS Shell and Utilities. The SAS/C Compiler enables you to develop applications that can be invoked from either the traditional OS/390 environment or the USS shell.

Applications that reside in an OS/390 data set are invoked with the CALL command from the TSO/E environment or with JCL statements and the SUBMIT command in a batch environment. They can also be invoked from the shell using the pdscall shell command.
Applications that reside in an USS HFS file are usually invoked directly from the USS shell, and can be run either interactively or in the background.

The USS hierarchical file system and shell provide an operating system interface that complies with the POSIX 1003.1 standard. With Release 6.00, the SAS/C Library provides a number of functions that give you the capability of exploiting the functionality of this interface. USS OS/390 and the SAS/C Library also implement portions of the draft POSIX 1003.1a standard. The support provided for these two standards is referred to as POSIX.1 and POSIX.1a in this documentation.

The POSIX.1 standard defines an operating system interface and environment that is based on the UNIX operating system. Many of the commands and features of the USS shell will be familiar to you if you have studied UNIX. The portable operating system interface (POSIX) was designed to support application portability at the source level.

What is a POSIX Application?

A POSIX application can be considered to be any application that takes advantage of the POSIX.1 and POSIX.1a support provided by the SAS/C Library. As will be explained later in this chapter, there are various levels of conformance to the POSIX.1 standards, ranging from strict conformance to a rather loose conformance that takes advantage of the extensions provided by the SAS/C Library. A POSIX application may have any of these levels of conformance to the POSIX.1 standards.

POSIX References

The SAS/C documentation does not describe the POSIX.1 standard or cover the general background concepts required to successfully develop a POSIX application. For information on these topics, please refer to the following publications:

ISO/IEC 9945-1: 1990 (IEEE Std 1003.1-1990)
Information technology--Portable Operating System Interface
(POSIX)--Part 1: System Application Program Interface (API)
[C Language]

Zlotnick, Fred (1991) The POSIX.1 Standard: A Programmer's guide,
The Benjamin/Cummings Publishing Company, Inc.

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