Control Language Programming for the As/400 - Softcover

Meyers, Bryan; Riehl, Dan

Softcover

ISBN 10: 1882419766 ISBN 13: 9781882419760

Publisher: 29th Street Pr, 1997

Synopsis

A text for students planning careers as AS/400 programmers, assuming no prior knowledge of Control Language (CL). Material for a 13-session course is covered in five sections on introducing CL, basic CL programming, I/O in a CL program, advanced CL programming, and creating commands. Chapters end with key terms, review questions, exercises, and graduated programming assignments. Sidebars offer tips on style issues. Appendices cover essentials of AS/400 features needed for program development and SEU, and offer a reference to CL commands. This second edition is updated to include discussion of the Integrated Language Environment (ILE) and its impact on traditional AS/400 concepts, and contains an appendix on the ILE debugger. Annotation c. by Book News, Inc., Portland, Or.

About this title

About the Author

Bryan Meyers, CCP, is director of information services for KOA Kampgrounds of America and a senior technical editor for NEWS/400. Bryan has more than 25 years of consulting, programming, and system design experience in the IBM midrange arena. He is the author if RPG IV Jump Start, 2nd edition, published by 29th Street Press.

Dan Riehl is a technical editor for NEWS/400 and president of PowerTech Toolworks, Inc., a Seattle-based firm providing AS/400 technical education and support. Dan also is the editor of Power Tools for the AS/400 and the author of Desktop Guide to AS/400 Programmer's Tools, published by 29th Street Press.

From the Inside Flap

Since its introduction in 1993, Control Language Programming for the AS/400 has become an integral part of hundreds of AS/400 college courses. The textbook has proven to be a boon to students who plan to initiate careers as AS/400 programming professionals, as well as a must-read for programmers already in the AS/400 workforce who need to brush up on their CL techniques.

In this second edition, Bryan Meyers and Dan Riehl have updated the text to include discussion of the Integrated Language Environment (ILE). Specifically, Chapter 22 discusses fundamental changes ILE introduces to the AS/400’s execution model. This chapter will help the student understand how ILE has changed some traditional AS/400 concepts. In addition, a new appendix explains how to use the ILE debugger.

The authors, with more than 20 years’ experience in CL programming between them, write from an up-to-the minute knowledge of the skills required in today’s MIS environment.

Students without previous knowledge of CL will learn the basics quickly. As the book progresses methodically to more complex processes and concepts, it guides readers smoothly toward a professional grasp of CL programming techniques and style.

Control Language Programming for the AS/400, Second Edition, is organized into five sections containing 25 chapters. Each chapter ends with review questions and practical exercises and includes graduated programming assignments. Throughout, concise “Coding in Style” sidebars offer tips on style issues that give students the benefit of the authors’ years of practical experience. Two appendices cover essentials of AS/400 features needed for program development and SEU. A third appendix serves as a condensed reference to the CL commands used most often in CL programs.

Excerpt. © Reprinted by permission. All rights reserved.

1.1. What CL Is

AS/400 Control Language (CL) is a set of commands that you use to control operations and to request system-related functions on the IBM AS/400 computer. IBM provides CL as an integrated part of the OS/400 operating system, not as a separate product.

As a means of controlling workflow, CL serves purposes comparable to Job Control Language (JCL) on mainframe computers. CL, however, provides much more functionality than JCL. In some respects, CL is similar to the PC-DOS (Disk Operating System) commands you may use on a PC. DOS operations like copying files, redirecting output, and making directories have direct CL counterparts. CL originated on the IBM System/38 computer in the late 1970s and continued as the principal system control language when the AS/400 was introduced in 1988. The AS/400 version of CL provided many enhancements over the S/38 version, including new commands and other added functionality. However, because of similarities between the S/38 and AS/400 versions of CL, many S/38 CL commands and programs can be used on the AS/400, and vice versa.

A single CL statement is called a command. A CL command is the primary means of interacting with the AS/400. Nearly everything the AS/400 does is requested by a command. There are commands to create and delete objects, commands to start programs, a command to power down the system, and even a command to create a command.

You can think of a command as an instruction to the computer to perform a function. For example, the DLTF (Delete File) command instructs the AS/400 to delete a file from the system; this command would be comparable to the DEL command, which is a part of DOS on personal computers.

Most CL commands are supplied by IBM as part of the operating system, but you also can create your own commands, customized to your own installation s particular needs.

CL, as shipped by IBM, consists of more than 1,000 commands but still maintains a usefulconsistency that makes the language easy to learn and to understand. Most CL commands can be used at least two ways: (1) by typing them individually onto an AS/400 command line, or (2) by grouping them together into a CL program. CL programs typically consist of multiple CL commands that define procedures or operations on the AS/400. By combining multiple commands within a CL program you can automate most AS/400 operations.

You should write CL programs to perform repetitive processing, because CL programs will reduce errors and operator/user intervention. CL also is a natural choice for many utility programs that control or monitor system-related activities on the AS/400. Figure 1.1 lists a few of the many functions that CL can perform.

1.2. What CL Is Not

Although CL is very rich in function, it is not in the classical sense of the term considered to be a high-level language (HLL). You would not, for example, write a payroll application using CL exclusively. For such application programming on the AS/400, you would use a combination of CL and a HLL such as RPG or COBOL. You would use CL to implement the system-related procedures and functions of the application and you would use the HLL to perform such operations as screen handling, file updates, and complex business logic. CL is used to manipulate and control the application s execution environment, generally as a front end to the HLL application programs.

Why wouldn t you use CL exclusively to create a typical business application? Because many functions perform better or are easier to write using a HLL, and CL just cannot do some computer operations. For example, CL programs cannot add or update records in a database file and CL has very limitedprinting capabilities.. CL programs do not support the use of AS/400 subfiles within application displays, nor do they support individual fields in AS/400 program-described files. Database manipulations are limited to reading files and only a single file can be opened for I/O operations in a CL program. These missing pieces in CL make it unsuitable for developing a complete business application.

1.3. Controlling Workflow with CL

CL programs control the workflow of an application by allowing you to create jobstreams, which consist of CL commands to be executed in order. Within a CL program you can alter the order of execution by testing various conditions that may exist during the execution of a job. You can monitor for errors that might occur while running a job and perform corrective actions or abort the job. You can pass values, or parameters, to and from CL programs to make them more flexible and to permit or restrict the execution of blocks of program code. A CL program can incorporate conditional logic and special functions that are not available when you enter individual commands on a command line. You can also test and debug a CL program, just like any HLL program.

CL programs, unlike JCL , are implemented as compiled program objects, rather than interpreted job streams. A CL program is a permanent object on the AS/400, created by compiling a group of CL commands.

Edition details

• Publisher: 29th Street Pr
• Publication date: 1997
• Language: English
• ISBN 10: 1882419766
• ISBN 13: 9781882419760
• Binding: Paperback
• Number of pages: 522