Preface

An operating system is like an old friend. You may be in daily contact with him or only see him occasionally. Over the years a firm bond of friendship develops. You come to realize that he is not perfect, and still you feel comfortable with his idiosyncrasies. In short, you accept him for who he is.

OpenVMS, the traditional operating system used by many Digital Equipment Corporation (DEC) VAX and Alpha processors, is an old friend to many of us. However, you will likely need to learn a version of the UNIX operating system, for UNIX is the operating system of choice for most processors that use innovative hardware architectures. You may be attracted by the stability that UNIX provides as a development medium in a rapidly changing hardware market. After all, UNIX is the closest we have come to a generic operating system, suited to controlling a variety of hardwares from many vendors. Whatever your reasons for learning UNIX, if you are already familiar with OpenVMS, this may well be the book for you.

The book is intended to help you mold the interactive computing skills that you learned using OpenVMS into the skills necessary for computing in the UNIX framework. It is not meant to be a UNIX user's manual, nor is it designed to teach UNIX from first principles. The book draws upon the experience of observing professionals with varying degrees of Open- VMS expertise grapple with the concrete and philosophical issues of UNIX. This book emphasizes UNIX derived from Berkeley UNIX, or Berkeley Software Distribution (BSD), although many of the features discussed are pertinent to any version of UNIX. Both the C shell and the Korn shell, two of the most widely used command-line interfaces to UNIX, are discussed. Thus, this text should also be useful to those migrating from Open VMS to AIX, AT&T System V, Tru64 UNIX, HP-UX, Solaris, or any other version of UNIX.

Chapter 1 begins with a brief history of UNIX and Open VMS. The ideas underlying the conception of each operating system differ markedly. To a casual user, these differences result in a UNIX user interface that appears to be quite different from the Digital Command Language (DCL) interpreter under OpenVMS. Chapter 1 does not discuss any of these differences in detail; the remainder of the book does that. Rather, Chapter 1 explains how these differences came about and gives some of the reasons for them. At first glance, such a discussion may appear superfluous to the central task of learning a subset of useful UNIX commands. However, an understanding of how UNIX and OpenVMS have evolved lets one begin to see the more subtle differences between the two operating systems, differences exemplified throughout this book. For example, OpenVMS is designed as a series of powerful, self-contained commands that the user issues sequentially. UNIX, on the other hand, is designed to be modular, so that users piece together two or more simple modules to form a single complex command string. Thus, effective use of UNIX requires more than learning a new command syntax; it requires a new mode of thinking. The best way to introduce this new mode of thought is to try to capture what the original UNIX developers were thinking when they laid the foundations of UNIX. Chapter 1 ends with a brief consideration of the future directions of UNIX and OpenVMS, based on emerging standards.

Before your hands touch the keyboard, you must grasp a number of ideas that will help prevent later frustration. These ideas are the subject of Chapter 2. First and foremost are the particulars of how the UNIX shell actually interprets a command, in contrast to the OpenVMS command- language interpreter. This discussion introduces the concepts of pipes, filters, and input/output redirection, features that give great power to UNIX and that you need to build the complex command strings mentioned above. Second are the UNIX concepts of the disk partition and file system, in contrast to the OpenVMS physical device and directory. These UNIX concepts are particularly important for anyone interested in UNIX system management. UNIX and OpenVMS operating system internals (data structures, input/output subsystems, and system services) are compared in only a cursory fashion.

With the formalities out of the way, you are ready to move to the terminal and begin getting acquainted with your new friend. Chapter 3 introduces the basic commands and files governing every terminal session and indicates how they differ from those of OpenVMS. You will learn how to tailor the environment to get the most from each UNIX terminal session. Chapter 3 concludes with two topics that OpenVMS users making the transition to UNIX find the most irksome: the recall and cumbersome editing of command lines and the use of online help and the UNIX document set.

At this point, you should be yearning for some serious interactive computing. Chapter 4 introduces a subset of file-management commands that you are likely to need in the first few terminal sessions. So as not to bewilder the beginner, we leave the more complex file-management commands for Chapter 8. In Chapter 4, you should begin to comprehend the power of the UNIX environment.

Chapter 5 follows with a comparison of the most commonly used UNIX and OpenVMS line and screen editors in preparation for some meaningful application development. Chapter 5 also introduces two utilities available to OpenVMS users as part of the POSIX environment that offer powerful features for pattern matching and subsequent file modification.

At this stage, you should be ready to communicate with fellow users and systems staff. Chapter 6 covers the basic features of interactive communications and batch communications via e-mail. For the reader who must communicate with users on remote computers, Chapter 13 revisits e-mail as part of a discussion of processor-to-processor communications.

Chapter 7 introduces the UNIX equivalents of queuing batch and print requests and making tape-drive requests. There are no surprises for the OpenVMS user when it comes to printing files in UNIX, but the same can- not be said of magnetic tape and batch processing. The use of magnetic tapes in UNIX is in some ways arcane, but the real surprise is UNIX's inability to handle batch processing. Chapter 7 explains that this is not a shortcoming, but a difference in philosophy. UNIX has no need for batch queues, since you can easily manage multiple tasks interactively.

By the time you get to Chapter 8, you will need more complex file-management commands. Chapter 8 builds upon the introductory discussion of file management in Chapter 4 by introducing new commands and options.

Chapter 9 discusses programming using a high-level language in the UNIX environment and provides insight into the programming tools for which UNIX is renowned, some of which are available as layered products under OpenVMS. Chapter 9 discusses tools for debugging, profiling, and maintaining large programs with examples from the C and FORTRAN languages.

In UNIX, programming is not restricted to a high-level language inasmuch as you can write programs using the user interface, or shell. Chapter 10 discusses features of shell programming and how it compares to writing OpenVMS command procedures.

Managing user and group accounts, installing software, managing networks, and other tasks are the responsibility of the system administrator. Chapter 11 discusses these and other tasks.

Effective use of any computer system requires an examination of how system resources are being consumed. Chapter 12 describes how to perform such an examination of the UNIX environment.

Finally, Chapter 13 discusses the use of UNIX in a distributed environment of UNIX or UNIX and OpenVMS processors. It considers connections both by fast dedicated networks and by slower asynchronous modems. The chapter groups network communications on the basis of trusted-host access—the UNIX equivalent to a proxy login. Chapter 13 includes a brief discussion of the Network File System (NFS).

Appendixes A and B summarize all we have learned by means of cross- reference tables that compare OpenVMS and UNIX commands and editor functions. The tables also provide the section number where you may find a detailed discussion of each command. Appendix C summarizes the various UNIX files introduced throughout the text. Appendix D is anomalous to the rest of the book, being a procedure to convert existing OpenVMS mail files to a common format used by UNIX mail handlers. Appendix E provides references to Web sites for further information.

While this book will give you basic competency in many areas of UNIX, we have included a bibliography for those who need a different perspective or a deeper understanding. Many will find the Web-based references invaluable as they sit by the keyboard wondering what to do next.

The text emphasizes the practical aspects of UNIX throughout. It is loaded with everyday examples of performing tasks, each of which is compared to its closest OpenVMS counterpart. Where no counterpart exists, that fact is noted. If you have some familiarity with the OpenVMS example presented and compare it to the UNIX example and read the explanation, you should become a competent UNIX user in a short time.

Both operating systems are so rich in their versatility and functionality that producing a concise text meant making some harsh decisions about what should be included and...