Book excerpt: The AS/400 Control Language (CL) is a set of commands that provide the primary interface between users and the system. Collectively, CL has more than a thousand commands, each of which is designed to perform a specific system, operational, or programming task. This book is a complete tutorial and easy-to-use reference for the AS/400 control language, together with AS/400: SYSTEM, UTILITIES, DATABASE AND PROGRAMMING by Lin & Stewart, it forms a complete tutorial and reference package for the AS/400.* covers CL commands, CL programming fundamentals, CL programming elements, calling programs and processing files, and advanced topics, such as sending messages and debugging programs.