- Taschenbuch: 432 Seiten
- Verlag: O'Reilly and Associates; Auflage: 2 (1. März 1997)
- Sprache: Englisch
- ISBN-10: 1565922255
- ISBN-13: 978-1565922259
- Größe und/oder Gewicht: 17,8 x 2,5 x 23,3 cm
- Durchschnittliche Kundenbewertung: 20 Kundenrezensionen
- Amazon Bestseller-Rang: Nr. 33.048 in Fremdsprachige Bücher (Siehe Top 100 in Fremdsprachige Bücher)
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sed & awk (In a Nutshell) (Englisch) Taschenbuch – 1. März 1997
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sed & awk describes two text processing programs that are mainstays of the UNIX programmer's toolbox. sed is a "stream editor" for editing streams of text that might be too large to edit as a single file, or that might be generated on the fly as part of a larger data processing step. The most common operation done with sed is substitution, replacing one block of text with another. awk is a complete programming language. Unlike many conventional languages, awk is "data driven" -- you specify what kind of data you are interested in and the operations to be performed when that data is found. awk does many things for you, including automatically opening and closing data files, reading records, breaking the records up into fields, and counting the records. While awk provides the features of most conventional programming languages, it also includes some unconventional features, such as extended regular expression matching and associative arrays. sed & awk describes both programs in detail and includes a chapter of example sed and awk scripts. This edition covers features of sed and awk that are mandated by the POSIX standard.This most notably affects awk, where POSIX standardized a new variable, CONVFMT, and new functions, toupper() and tolower(). The CONVFMT variable specifies the conversion format to use when converting numbers to strings (awk used to use OFMT for this purpose). The toupper() and tolower() functions each take a (presumably mixed case) string argument and return a new version of the string with all letters translated to the corresponding case. In addition, this edition covers GNU sed, newly available since the first edition. It also updates the first edition coverage of Bell Labs nawk and GNU awk (gawk), covers mawk, an additional freely available implementation of awk, and briefly discusses three commercial versions of awk, MKS awk, Thompson Automation awk (tawk), and Videosoft (VSAwk).
The book begins with an overview and a tutorial that demonstrate a progression in functionality from grep to sed to awk. sed and awk share a similar command-line syntax, accepting user instructions in the form of a script. Because all three programs use UNIX regular expressions, an entire chapter is devoted to understanding UNIX regular expression syntax. Next, the book describes how to write sed scripts. After getting started by writing a few simple scripts, you'll learn other basic commands that parallel manual editing actions, as well as advanced commands that introduce simple programming constructs. Among the advanced commands are those that manipulate the hold space, a set-aside temporary buffer. The second part of the book has been extensively revised to include POSIX awk as well as coverage of three freely available and three commercial versions of awk. The book introduces the primary features of the awk language and how to write simple scripts. You'll also learn: common programming constructs; how to use awk's built-in functions; how to write user-defined functions; debugging techniques for awk programs; how to develop an application that processes an index, demonstrating much of the power of awk; and FTP and contact information for obtaining various versions of awk. Also included is a miscellany of user-contributed scripts that demonstrate a wide range of sed and awk scripting styles and techniques.|
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But there is so much more these two tools can do. And this book shows you how. In each of the two major parts things are laid out in a logical manner building up knowledge thoroughly from the ground up, all supported by lots of well explained examples.
Both, sed and awk, rely heavily on regular expressions and the authors don't let you down in this area either. Chapter 3 is dedicated to equip you with a well enough working knowledge of regular expressions. It surely is not as thorough as Jeffry Friedl's "Mastering Regular Expressions", but the chapter packs a lot of information into the 29 pages. Especially with awk, there are quite a number of different versions out there and they are not quite identical in feature scope. Differences among some major implementations are discussed as well. Finally, in the appendices, you can find a quick reference for both sed and awk.
As thorough (and even beginner friendly) as the book is, it does have one drawback: it is old. Much of the sample code deals with manipulating troff files or uucp logs. Both things many unix/linux users of today have no idea about. The reliance on such old samples is not a problem per se, they still do the job of demonstrating concepts and usage of sed and awk quite nicely. But these samples are much less applicable to sed/awk users today than they were twenty years ago when the first edition of this book was published. What I also think would be badly needed in an updated third revision is a discussion of how to use these tools with non-English charactersets and Unicode.
While this is an excellent book for learning to use sed and awk much more effectively, let's hope that the authors sometime get around to do an overhaul, provide samples which are more accessible today and also add a chapter or two about using these tools with the much larger and inherently more complex charactersets in common use today.
Plain, understandable language, very good tutorial. Keep "Unix in a nutshell" close, if you ned sed and awk references, because that's not what this book is good for.
Someone here said that this book saved him from carpal tunnel, and believe him, it will also save YOU. ;-)
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