ISO/IEC/IEEE 9945:2009定义了标准操作系统接口和环境，包括命令解释器（或“shell”）和通用实用程序，以支持源代码级别的应用程序可移植性。ISO/IEC/IEEE 9945:2009旨在供应用开发者和系统实施者使用，并且包括四个主要组件（每个组件在相关卷中）。 本标准所有卷共有的通用术语、概念和接口，包括实用程序约定和C语言标题定义，都包含在基本定义卷中。 系统服务函数和子程序的定义、C编程语言的特定语言系统服务、函数问题（包括可移植性、错误处理和错误恢复）都包含在系统接口卷中。命令解释服务的标准源代码级接口（“shell”）和应用程序的通用实用程序的定义包含在shell和实用程序卷中。 扩展的基本原理不适合文档结构的其余部分，其中包含有关ISO/IEC/IEEE 9945:2009内容的历史信息，以及为什么ISO/IEC/IEEE 9945:2009开发人员包含或丢弃功能，包含在基本原理（信息）卷中。 以下领域超出了ISO/IEC/IEEE 9945:2009的范围: 图形界面； 数据库管理系统接口； 记录I/O注意事项； 对象或二进制代码可移植性； 系统配置和资源可用性。 ISO/IEC/IEEE 9945:2009描述了对应用程序开发人员重要的外部特性和设施，而不是用于实现这些功能的内部构造技术。特别强调各种商业应用所需的功能和设施。

ISO/IEC/IEEE 9945:2009 defines a standard operating system interface and environment, including a command interpreter (or "shell"), and common utility programs to support applications portability at the source code level. ISO/IEC/IEEE 9945:2009 is intended to be used by both application developers and system implementers and comprises four major components (each in an associated volume).

• General terms, concepts, and interfaces common to all volumes of this standard, including utility conventions and C-language header definitions, are included in the Base Definitions volume.
• Definitions for system service functions and subroutines, language-specific system services for the C programming language, function issues, including portability, error handling, and error recovery, are included in the System Interfaces volume.
• Definitions for a standard source code-level interface to command interpretation services (a "shell") and common utility programs for application programs are included in the Shell and Utilities volume.
• Extended rationale that did not fit well into the rest of the document structure, which contains historical information concerning the contents of ISO/IEC/IEEE 9945:2009 and why features were included or discarded by the ISO/IEC/IEEE 9945:2009 developers, is included in the Rationale (Informative) volume.

The following areas are outside the scope of ISO/IEC/IEEE 9945:2009:

• graphics interfaces;
• database management system interfaces;
• record I/O considerations;
• object or binary code portability;
• system configuration and resource availability.

ISO/IEC/IEEE 9945:2009 describes the external characteristics and facilities that are of importance to application developers, rather than the internal construction techniques employed to achieve these capabilities. Special emphasis is placed on those functions and facilities that are needed in a wide variety of commercial applications.