GAWK: Effective AWK Programming

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viiiGAWK: Effective AWK ProgrammingB.3.1.6 Using gawk In The MSYS Environment . . . . . . . . . . . . 275B.3.2 How to Compile and Install gawk on VMS . . . . . . . . . . . . . . 275B.3.2.1 Compiling gawk on VMS . . . . . . . . . . . . . . . . . . . . . . . . . . . 275B.3.2.2 Installing gawk on VMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276B.3.2.3 Running gawk on VMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276B.3.2.4 Building and Using gawk on VMS POSIX . . . . . . . . . . 277B.3.2.5 Some VMS Systems Have An Old Version of gawk . . 277B.4 Unsupported Operating System Ports. . . . . . . . . . . . . . . . . . . . . . . . 277B.4.1 Installing gawk on the Atari ST . . . . . . . . . . . . . . . . . . . . . . . . . 277B.4.1.1 Compiling gawk on the Atari ST . . . . . . . . . . . . . . . . . . . 278B.4.1.2 Running gawk on the Atari ST . . . . . . . . . . . . . . . . . . . . . 278B.4.2 Installing gawk on BeOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279B.4.3 Installing gawk on a Tandem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279B.5 Reporting Problems and Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280B.6 Other Freely Available awk Implementations . . . . . . . . . . . . . . . . . 281Appendix C Implementation Notes . . . . . . . . . . 284C.1 Downward Compatibility and Debugging. . . . . . . . . . . . . . . . . . . . . 284C.2 Making Additions to gawk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284C.2.1 Adding New Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284C.2.2 Porting gawk to a New Operating System . . . . . . . . . . . . . . . 286C.3 Adding New Built-in Functions to gawk . . . . . . . . . . . . . . . . . . . . . . 287C.3.1 A Minimal Introduction to gawk Internals . . . . . . . . . . . . . . . 287C.3.2 Directory and File Operation Built-ins . . . . . . . . . . . . . . . . . . 292C.3.2.1 Using chdir and stat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292C.3.2.2 C Code for chdir and stat . . . . . . . . . . . . . . . . . . . . . . . . 293C.3.2.3 Integrating the Extensions . . . . . . . . . . . . . . . . . . . . . . . . . 296C.4 Probable Future Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297Appendix D Basic Programming Concepts . . 300D.1 What a Program Does. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300D.2 Data Values in a Computer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301D.3 Floating-Point Number Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302D.3.1 The String Value Can Lie. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302D.3.2 Floating Point Numbers Are Not Abstract Numbers . . . . 303D.3.3 Standards Versus Existing Practice . . . . . . . . . . . . . . . . . . . . . 304Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306GNU General Public License . . . . . . . . . . . . . . . . . . . 316GNU Free Documentation License . . . . . . . . . . . . . 327ADDENDUM: How to use this License for your documents . . . . . . . . 333Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
Foreword 1ForewordArnold Robbins and I are good friends. We were introduced 11 years ago by circumstances—and our favorite programming language, AWK. The circumstances started a couple of yearsearlier. I was working at a new job and noticed an unplugged Unix computer sitting in thecorner. No one knew how to use it, and neither did I. However, a couple of days later itwas running, and I was root and the one-and-only user. That day, I began the transitionfrom statistician to Unix programmer.On one of many trips to the library or bookstore in search of books on Unix, I foundthe gray AWK book, a.k.a. Aho, Kernighan and Weinberger, The AWK ProgrammingLanguage, Addison-Wesley, 1988. AWK’s simple programming paradigm—find a pattern inthe input and then perform an action—often reduced complex or tedious data manipulationsto few lines of code. I was excited to try my hand at programming in AWK.Alas, the awk on my computer was a limited version of the language described in theAWK book. I discovered that my computer had “old awk” and the AWK book described“new awk.” I learned that this was typical; the old version refused to step aside or relinquishits name. If a system had a new awk, it was invariably called nawk, and few systems had it.The best way to get a new awk was to ftp the source code for gawk from prep.ai.mit.edu.gawk was a version of new awk written by David Trueman and Arnold, and available underthe GNU General Public License.(Incidentally, it’s no longer difficult to find a new awk. gawk ships with Linux, and youcan download binaries or source code for almost any system; my wife uses gawk on her VMSbox.)My Unix system started out unplugged from the wall; it certainly was not plugged intoa network. So, oblivious to the existence of gawk and the Unix community in general, anddesiring a new awk, I wrote my own, called mawk. Before I was finished I knew about gawk,but it was too late to stop, so I eventually posted to a comp.sources newsgroup.A few days after my posting, I got a friendly email from Arnold introducing himself.He suggested we share design and algorithms and attached a draft of the POSIX standardso that I could update mawk to support language extensions added after publication of theAWK book.Frankly, if our roles had been reversed, I would not have been so open and we probablywould have never met. I’m glad we did meet. He is an AWK expert’s AWK expert and agenuinely nice person. Arnold contributes significant amounts of his expertise and time tothe Free Software Foundation.This book is the gawk reference manual, but at its core it is a book about AWK programmingthat will appeal to a wide audience. It is a definitive reference to the AWK languageas defined by the 1987 Bell Labs release and codified in the 1992 POSIX Utilities standard.On the other hand, the novice AWK programmer can study a wealth of practical programsthat emphasize the power of AWK’s basic idioms: data driven control-flow, patternmatching with regular expressions, and associative arrays. Those looking for somethingnew can try out gawk’s interface to network protocols via special ‘/inet’ files.The programs in this book make clear that an AWK program is typically much smallerand faster to develop than a counterpart written in C. Consequently, there is often a payoffto prototype an algorithm or design in AWK to get it running quickly and expose problems
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