sed and awk

( 40 )

Overview

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...
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Overview

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.


Serious UNIX programmers and administrators will enjoy the second edition of this best-selling book on a set of the most popular UNIX utilities, sed and awk. Why? Because it covers awk as described by the POSIX standard as well as NetBSD, FreeBSD, and the Linux versions of awk.

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Editorial Reviews

From Barnes & Noble

Fatbrain Review

Serious UNIX programmers and administrators will enjoy the second edition of this best-selling book on a set of the most popular UNIX utilities, sed and awk. Why? Because it covers awk as described by the POSIX standard as well as NetBSD, FreeBSD, and the Linux versions of awk.

The journey begins with an overview of the basic operations of sed and awk, showing a progression in functionality from grep to sed to awk. The next stop is writing sed scripts. You'll learn the syntax of sed commands, and advanced features, including multiple pattern space and hold space commands.

The book then moves to writing scripts for awk. Discussions include pattern matching, expressions, relational and Boolean operators, and informal retrieval. The text also explains awk's built-in functions and user-defined functions. The authors keep you learn by outlining the development of an index processing application, and they offer the readers contact information on how to obtain various versions of awk. This tutorial includes a miscellany of sed and awk scripting styles and techniques.

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Product Details

  • ISBN-13: 9781565922259
  • Publisher: O'Reilly Media, Incorporated
  • Publication date: 3/28/1997
  • Series: Nutshell Handbooks Series
  • Edition description: Second Edition
  • Edition number: 2
  • Pages: 434
  • Sales rank: 523,911
  • Product dimensions: 9.00 (w) x 7.00 (h) x 1.00 (d)

Meet the Author

Dale Dougherty is the publisher of the O'Reilly Network and Director of O'Reilly Research. Dale has been instrumental in many of O'Reilly's most important efforts, including founding O'Reilly & Associates with Tim O'Reilly. He was the developer and publisher of Global Network Navigator (GNN), the first commercial Web site. Dale was developer and publisher of Web Review, the online magazine for Web designers, and he was O'Reilly & Associates' first editor. Dale has written and edited numerous books at O'Reilly & Associates. Dougherty is a Lecturer in the School of Information Management and Systems (SIMS) at the University of California at Berkeley.

Arnold Robbins, an Atlanta native, is a professional programmer and technical author. He has worked with Unix systems since 1980, when he was introduced to a PDP-11 running a version of Sixth Edition Unix. He has been a heavy AWK user since 1987, when he became involved with gawk, the GNU project's version of AWK. As a member of the POSIX 1003.2 balloting group, he helped shape the POSIX standard for AWK. He is currently the maintainer of gawk and its documentation. He is also coauthor of the sixth edition of O'Reilly's Learning the vi Editor. Since late 1997, he and his family have been living happily in Israel.

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Read an Excerpt


From Chapter 7: Writing Scripts for awk

As mentioned in the preface, this book describes POSIX awk; that is, the awk language as specified by the POSIX standard. Before diving into the details, we'll provide a bit of history.

The original awk was a nice little language. It first saw the light of day with Version 7 UNIX, around 1978. It caught on, and people used it for significant programming.

In 1985, the original authors, seeing that awk was being used for more serious programming than they had ever intended, decided to beef up the language. (See Chapter 11, A Flock of awks, for a description of the original awk, and all the things it did not have when compared to the new one.) The new version was finally released to the world at large in 1987, and it is this version that is still found on SunOS 4.1.x systems.

In 1989, for System V Release 4, awk was updated in some minor ways. This version became the basis for the awk feature list in the POSIX standard. POSIX clarified a number of things about awk, and added the CONVFMT variable (to be discussed later in this chapter).

As you read the rest of this book, bear in mind that the term awk refers to POSIX awk, and not to any particular implementation, whether the original one from Bell Labs, or any of the others discussed in Chapter 11. However, in the few cases where different versions have fundamental differences of behavior, that will be pointed out in the main body of the discussion.

Playing the Game

To write an awk script, you must become familiar with the rules of the game. The rules can be stated plainly and you will find them described in Appendix B, QuickReference for awk, rather than in this chapter. The goal of this chapter is not to describe the rules but to show you how to play the game. In this way, you will become acquainted with many of the features of the language and see examples that illustrate how scripts actually work. Some people prefer to begin by reading the rules, which is roughly equivalent to learning to use a program from its manual page or learning to speak a language by scanning its rules of grammar--not an easy task. Having a good grasp of the rules, however, is essential once you begin to use awk regularly. But the more you use awk, the faster the rules of the game become second nature. You learn them through trial and error--spending a long time trying to fix a silly syntax error such as a missing space or brace has a magical effect upon long-term memory. Thus, the best way to learn to write scripts is to begin writing them. As you make progress writing scripts, you will no doubt benefit from reading the rules (and rereading them) in Appendix B or the awk manpage or The AWK Programming Language book. You can do that later--let's get started now.

Hello, World

It has become a convention to introduce a programming language by demonstrating the "Hello, world" program. Showing this program works in awk will demonstrate just how unconventional awk is. In fact, it's necessary to show several different approaches to printing "Hello, world."

In the first example, we create a file named test that contains a single line. This example shows a script that contains the print statement:

$ echo 'this line of data is ignored' > test
$ awk '{ print "Hello, world" }' test

Hello, world

This script has only a single action, which is enclosed in braces. That action is to execute the print statement for each line of input. In this case, the test file contains only a single line; thus, the action occurs once. Note that the input line is read but never output.

Now let's look at another example. Here, we use a file that contains the line "Hello, world."

$ cat test2
Hello, world
$ awk '{ print }&39; test2
Hello, world

In this example, "Hello, world" appears in the input file. The same result is achieved because the print statement, without arguments, simply outputs each line of input. If there were additional lines of input, they would be output as well.

Both of these examples illustrate that awk is usually input-driven. That is, nothing happens unless there are lines of input on which to act. When you invoke the awk program, it reads the script that you supply, checking the syntax of your instructions. Then awk attempts to execute the instructions for each line of input. Thus, the print statement will not be executed unless there is input from the file.

To verify this for yourself, try entering the command line in the first example but omit the filename. You'll find that because awk expects input to come from the keyboard, it will wait until you give it input to process: press RETURN several times, then type an EOF (CTRL-D on most systems) to signal the end of input. For each time that you pressed RETURN, the action that prints "Hello, world" will be executed.

There is yet another way to write the "Hello, world" message and not have awk wait for input. This method associates the action with the BEGIN pattern. The BEGIN pattern specifies actions that are performed before the first line of input is read.

$ awk 'BEGIN { print "Hello, world" }'
Hello, world

Awk prints the message, and then exits. If a program has only a BEGIN pattern, and no other statements, awk will not process any input files.

Awk's Programming Model

It's important to understand the basic model that awk offers the programmer. Part of the reason why awk is easier to learn than many programming languages is that it offers such a well-defined and useful model to the programmer.

An awk program consists of what we will call a main input look. a loop is a routine that is executed over and over again until some condition exists that terminates it. You don't write this loop, it is given--it exists as the framework within which the code that you do write will be executed. The main input loop in awk is a routine that reads one line of input from a file and makes it available for processing. The actions you write to do the processing assume that there is a line of input available. In another programming language, you would have to create the main input loop as part of your program. It would have to open the input file and read one line at a time. This is not necessary a lot of work, but it illustrates a basic awk shortcut and makes it easier for you to write your program.

The main input loop is executed as many times as there are lines of input. As you saw in the "Hello, world" examples, this loop does not execute until there is a line of input. It terminates when there is no more input to be read.

Awk allows you to write two special routines that can be executed before any input is read and after all input is read. These are the procedures associated with the BEGIN and END rules, respectively. In other words, you can do some preprocessing before the main input loop is ever executed and you can do some postprocessing after the main input loop has terminated. The BEGIN and END procedures are optional.

You can think of an awk script as having potentially three major parts: what happens before, what happens during, and what happens after processing the input. Figure 7-1 shows the relationship of these parts in the flow of control of an awk script...

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Table of Contents

Dedication

Preface

Chapter 1: Power Tools for Editing

Chapter 2: Understanding Basic Operations

Chapter 3: Understanding Regular Expression Syntax

Chapter 4: Writing sed Scripts

Chapter 5: Basic sed Commands

Chapter 6: Advanced sed Commands

Chapter 7: Writing Scripts for awk

Chapter 8: Conditionals, Loops, and Arrays

Chapter 9: Functions

Chapter 10: The Bottom Drawer

Chapter 11: A Flock of awks

Chapter 12: Full-Featured Applications

Chapter 13: A Miscellany of Scripts

Appendix A: Quick Reference for sed

Appendix B: Quick Reference for awk

Appendix C: Supplement for Chapter 12

Colophon

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Introduction

This book is about a set of oddly named UNIX utilities sed and awk. These utilities have many things in common, including the use of regular expressions for pattern matching. Since pattern matching is such an important part of their use, this book explains UNIX regular expression syntax very thoroughly. Because there is a natural progression in learning from grep to sed to awk, we will be covering all three programs, although the focus is on sed and awk.

Sed and awk are tools used by users, programmers, and system administrators_ anyone working with text files. Sed, so called because it is a stream editor, is perfect for applying a series of edits to a number of files. Awk, named after its developers Aho,, Weinberger,, and Kernighan,, is a programming language that permits easy manipulation of structured data and the generation of formatted reports. This book emphasizes the POSIX definition of awk. In addition, the book briefly describes the original version of awk, before discussing three freely available versions of awk and two commercial ones, all of which implement POSIX awk.

The focus of this book is on writing scripts for sed and awk that quickly solve an assortment of problems for the user. Many of these scripts could be called "quickfixes." In addition, we'll cover scripts that solve larger problems that require more careful design and development.

Scope of This Handbook
Chapter 1, Power Tools for Editing, is an overview of the features and capabilities of sed and awk.

Chapter 2, Under standing, Basic Operations, demonstrates the basic operations of sed and awk, showing a progression in functionality from sed to awk. Both share a similarcommand-line syntax, accepting user instructions in the form of a script.

Chapter 3, Understanding Regular Expression Syntax, describes UNIX regular expression syntax in full detail. New users are often intimidated by these strange expressions, used for pattern matching. It is important to master regular expression syntax to get the most from sed and awk. The pattern-matching examples in this chapter largely rely on grep and egrep.

Chapter 4, Writing sed Scripts, begins a three-chapter section on sed. This chapter covers the basic elements of writing a sed script using only a few sed commands. It also presents a shell script that simplifies invoking sed scripts.

Chapter 5, Basic sed Commands and Chapter 6, Advanced sed Commands, divide the sed command set into basic and advanced commands. The basic commands are commands that parallel manual editing actions, while the advanced commands introduce simple programming capabilities. Among the advanced commands are those that manipulate the hold space, a set-aside temporary buffer.

Chapter 7, Writing Scripts for awk, begins a five-chapter section on awk. This chapter presents the primary features of this scripting language. A number of scripts are explained, including one that modifies the output of the ls command.

Chapter 8, Conditionals' Loops, and Arrays, describes how to use common programming constructs such as conditionals, loops, and arrays.

Chapter 9, Functions, describes how to use awk's built-in functions as well as how to write user-defined functions.

Chapter 10, The Bottom Drawer, covers a set of miscellaneous awk topics. It describes how to execute UNIX commands from an awk script and how to direct output to files and pipes. It then offers some (meager) advice on debugging awk scripts.

Chapter 11, A Flock of awks, describes the original V7 version of awk, the current Bell Labs awk, GNU awk (gawk) from the Free Software Foundation, and mawk, by Michael Brennan. The latter three all have freely available source code. This chapter also describes two commercial implementations, MKS awk and Thomson Automation awk (tawk), as well as VSAwk, which brings awk-like capabilities to the Visual Basic environment.

Chapter 12, Full-Featured Applications presents two longer, more complex awk scripts that together demonstrate nearly all the features of the language. The first script is an interactive spelling checker. The second script processes and formats the index for a book or a master index for a set of books.

Chapter 13, A Miscellany of Scripts, presents a number of user-contributed scripts that show different styles and techniques of writing scripts for sed and awk.

Appendix A, Quick Reference for sea, is a quick reference describing sea's commands and command-line options.

Appendix B. Quick Reference for awk is a quick reference to awk's command-line options and a full description of its scripting language.

Appendix C, Supplement for Chapter 12, presents the full listings for the spellcheck.awk script and the masterindex shell script described in Chapter 12.

Availability of sed and awk
Sed and awk were part of Version 7 UNIX (also known as "V7," and "Seventh Edition") and have been part of the standard distribution ever since. Sed has been unchanged since it was introduced.

The Free Software Foundation GNU project's version of sed is freely available, although not technically in the public domain. Source code for GNU sed is available via anonymous FTP documentation. to the host ftp.gnu.ai.mit.edu. It is in the file /pub/gnu/sed-2.05.tar.gz. This is a tar file compressed with the gzip program, whose source code is available in the same directory. There are many sites worldwide that "mirror" the files from the main GNU distribution site; if you know of one close to you, you should get the files from there. Be sure to use "binary" or "image" mode to transfer the file(s).

In 1985, the authors of awk extended the language, adding many useful features. Unfortunately, this new version remained inside AT&T for several years. It became part of UNIX System V as of Release 3.1. It can be found under the name of nawk, for new awk; the older version still exists under its original name. This is still the case on System V Release 4 systems.

On commercial UNIX systems, such as those from Hewlett-Packard, Sun, IBM, Digital, and others, the naming situation is more complicated. All of these systems have some version of both old and new awk, but what each vendor names each program varies. Some have oawk and awk, others have awk and nawk. The best advice we can give is to check your local documentation. Throughout this book, we use the term awk to describe POSIX awk. Specific implementations will be referred to by name, such as "gawk," or "the Bell Labs awk."

Chapter 11 discusses three freely available awks (including where to get them), as well as several commercial ones.

DOS Versions
Gawk, mawk, and GNU sed have been ported to DOS. There are files on the main GNU distribution site with pointers to DOS versions of these programs. In addition, gawk has been ported to OS/2, VMS, and Atari and Amiga microcomputers, with ports to other systems (Macintosh, Windows) in progress.

egrep, sed, and awk are available for MS-DOS-based machines as part of the MKS Toolkit (Mortice Kern Systems, Inc., Ontario, Canada). Their implementation of awk supports the features of POSIX awk.

The MKS Toolkit also includes the Korn shell, which means that many shell scripts written for the Bourne shell on UNIX systems can be run on a PC. While most users of the MKS Toolkit have probably already discovered these tools in UNIX, we hope that the benefits of these programs will be obvious to PC users who have not ventured into UNIX.

Thompson Automation Software has an awk compiler for UNIX, DOS, and Microsoft Windows. This version is interesting because it has a number of extensions to the language, and it includes an awk debugger, written in awk!

We have used a PC on occasion because Ventura Publisher is a terrific formatting package. One of the reasons we like it is that we can continue to use vi to create and edit the text files and use sed for writing editing scripts. We have used sed to write conversion programs that translate troff macros into Ventura stylesheet tags. We have also used it to insert tags in batch mode. This can save having to manually tag repeated elements in a file.

Sed and awk are also useful for writing conversion programs that handle different file formats.

Other Sources of Information About sed and awk
For a long time, the main source of information on these utilities was two articles contained in Volume 2 of the UNIX Programmer's Guide. The article awk-A Pattern Scanning and Processing Language (September 1, 197X) was written by the language's three authors. In 10 pages, it offers a brief tutorial and discusses several design and implementation issues. The article SED-A Non-Interactive Text Editor (August 15, 1978) was written by Lee E. McMahon. It is a reference that gives a full description of each function and includes some useful examples (using Coleridge's Xanadu as sample input).

In trade books, the most significant treatment of sed and awk appears in The UNIX Programming Environment by Brian W. Kcrnighan and Rob Pike (Prentice-Hall, 1984). The chapter entitled "Filters" not only explains how these programs work but shows how they can work together to build useful applications.

The authors of awk collaborated on a book describing the enhanced version: The AWK Programming Language (Addison-Wesley, 1988). It contains many full examples and demonstrates the broad range of areas where awk can be applied. It follows in the style of the UNIX Programming Environment, which at times makes it too dense for some readers who are new users. The source code for the example programs in the book can be found in the directory /netlib/research/awkbookcode on netlib.bell-labs.com

The IEEE Standard for Information and Technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (Standard 1003.2-1992) describes both sed and awk. It is the "official" word on the features available for portable shell programs that use sed and awk. Since awk is a programming language in its own right, it is also the official word on portable awk programs.

In 1996, the Free Software Foundation published The GNU Awk User's Guide, by Arnold Robbins. This is the documentation for gawk, written in a more tutorial style than the Aho, Kernighan, and Weinberger book. It has two full chapters of examples, and covers POSIX awk. This book is also published by SSC under the title Effective AWKProgramming, and the Texinfo source for the book comes with the gawk distribution.

It is one of the current deficiencies of GNU sed that it has no documentation of its own, not even a manpage.

Most general introductions to UNIX introduce sed and awk in a long parade of utilities. Of these books, Henry McGilton and Rachel Morgan's Introducing the UNIX System offers the best treatment of basic editing skills, including use of all UNIX text editors.

UNIX Text Processing (Hayden Books, 1987), by the original author of this handbook and Tim O'Reilly, covers sed and awk in full, although we did not include the new version of awk. Readers of that book will find some parts duplicated in this book, but in general a different approach has been taken here. Whereas in the textbook we treat sed and awk separately, expecting only advanced users to tackle awk, here we try to present both programs in relation to one another. They are different tools that can be used individually or together to provide interesting opportunities for text processing.

Finally, in 1995 the Usenet newsgroup comp.lang.awk came into being. If you can't find what you need to know in one of the above books, you can post a question in the newsgroup, with a good chance that someone will be able to help you.

The newsgroup also has a "frequently asked questions" (FAQ) article that is posted regularly. Besides answering questions about awk, the FAQ lists many sites where you can obtain binaries of different versions of awk for different systems. You can retrieve the FAQ via FT P in the file called /pub/usenet/comp.lang.awk/faq from the host rtfm.mit.edu.

Sample Programs
The sample programs in this book were originally written and tested on a Mac IIci running A/UX 2.0 (UNIX System V Release 2) and a SparcStation 1 running SunOS 4.0. Programs requiring POSIX awk were re-testecl using gawk 3.0.0 as well as the August 1994 version of the Bell Labs awk from the Bell Labs FTP site (see Chapter 11 for the FTP details). Sed programs were retested with the SunOS 4.1.3 sed and GNU sed 2.05.

Obtaining Example Source Code
You can obtain the source code for the programs presented in this book from O'Reilly & Associates through their Internet server. The example programs in this book are available electronically in a number of ways: by FTP, Ftpmail, BITFTP, and UUCP. The cheapest, fastest, and easiest ways are listed first. If you read from the top down, the first one that works for you is probably the best. Use FTP if you are directly on the Internet. Use Ftpmail if you are not on the Internet, hut can

send and receive electronic mail to Internet sites (this includes CompuServe users). Use BITFTP if you can send electronic mail via BITNET. Use UUCP if none of the above works.

FTP
To use FTP, you need a machine with direct access to the Internet. A sample session is shown, with what you should type in boldface.

$ ftp ftp.ora.com
Connected to ftp.ora.com.
220 FTP server (Version 6.21 Tue Mar 10 22:09:55 EST 1992) ready.
Name (ftp.ora.com:yourname): anonymous
331 Guest login ok, send domain style e-mail address as password.
Password: yourname@domain .name (Use your user name and host here)
230 Guest login ok, access restrictions apply.
ftp> cd /published/oreilly/nuthell/sedawk_2
250 CWD command successful.
ftp> binary (Very important! You must specify binary transfer for compressed files.)
203 Type set to I.
ftp> get progs.tar.gz
200 PORT command successful.
150 Opening BINARY mode data connection for progs.tar.gz.
226 Transfer complete.
ftp> quit
221 Goodbye.

The file is a gzip compressed tar archive; extract the files from the archive by typing

$ gzcat progs.tar.gz | tar xvf -

System V systems require the following tar command instead:

$ gzcat progs . .tar. gz | tar xof

If gzcat is not available on your system, use separate gunzip and tar commands.

$ gunzip progs.tar.gz
$ tar xvf progs.tar

Ftpmail
Ftpmail is a mail server available to anyone who can send electronic mail to and receive it from Internet sites. This includes any company or service provider that allows email connections to the Internet. Here's how you do it. You send mail to ftpmail@online.ora.com. In the message body? give the FTP commands you want to run. The server will run anonymous FTP for you and mail the files back to you.

To get a complete help file, send a message with no subject and the single word "help" in the body. The following is a sample mail session that should get you the examples. This command sends you a listing of the files in the selected directory and the requested example files. The listing is useful if there's a later version of the examples you're interested in.

$ mail ftpmail@online.ora.com
Subject:
reply-to yourname@domain.name (Where you want files mailed)
open
cd /published/oreilly/nutshell/sedawk_2
dir
mode binary
uuencode
get progs.tar.gz
quit

A signature at the end of the message is acceptable as long as it appears after "quit."

BITFTP
BITFTP is a mail server for BITNET users. You send it electronic mail messages requesting files, and it sends you back the files by electronic mail. BITFTP currently serves only users who send it mail from nodes that are directly on BITNET, EARN, or NetNorth. To use BITFTP, send mail containing your ftp commands to BITFTP@PUCC. For a complete help file, send HELP as the message body. The following is the message body you send to BITFTP:

FTP ftp.ora.com NETDATA
USER anonymous
PASS yourname@yourhost.edu Put your Internet email address here (not your BITNET address)
CD /published/oreilly/nutshell/sedawk_2
DIR
BINARY
GET progs.tar.gz
QUIT

Once you've got the desired file, follow the directions under FTP to extract the files from the archive. Since you are probably not on a UNIX system, you may need to get versions of uudecode, gunzip, atob, and tar for your system. VMS, DOS, and Mac versions are available.

UUCP
UUCP is standard on virtually all UNIX systems and is available for IBM-compatible PCs and Apple Macintoshes. The examples are available by UUCP via modem from UUNET; UUNET's connect-time charges apply. If you or your company has an account with UUNET, you have a system somewhere with a direct UUCP connection to UUNET. Find that system, and type:

uucp uunet\ ! ~ /published/oreilly/nutshell/sedawk_2/progs. tar. gz yourhost\ ! ~ /yo urname/

The backslashes can be omitted if you use a Bourne-style shell (sh, ksh, bash, zsh, pdksh) instead of csh. The file should appear some time later (up to a day or more) in the directory /usr/spool/uucppublic/yourname. If you don't have an account, but would like one so that you can get electronic mail, contact UUNET at 703-206-5400. It's a good idea to get the file /publtshed/oreilly/ls-lR.Z as a short test file containing the filenames and sizes of all the files available. Once you've got the desired file, follow the directions under FT P to extract the files from the archive

Conventions Used in This Handbook
The following conventions are used in this hook:

Bold is used for statements and functions, identifiers, and program names.

Italic is used for file and directory names when they appear in the body of a paragraph as well as for data types and to emphasize new terms and concepts when they are introduced.

Constant Widthis used in examples to show the contents of files or the output from commands.

Constant Boldis used in examples to show command lines and options that should be typedliterally by the user. (For example, rm foo means to type "rm foo" exactly as itappears in the text or the example.)

"" are used to identify a code fragment in explanatory text. System messages and symbols are quoted as well.

$ is the UNIX Bourne shell or Korn shell prompt.

[ ] surrounds optional elements in a description of program syntax. (The brackets themselves should never be typed, unless otherwise noted.)

... stands for text (usually computer output) that's been omitted for clarity or to save space.

indicates a literal space. This symbol is used to make spaces visible in examples, as well as in the text.

indicates a literal TAB character. This symbol is used to make tabs visible in examples, as well as in the text.

The notation CTRL-X or ^X indicates use of control characters. It means hold down the "control" key while typing the character "x". We denote other keys similarly (e.g., RETURN indicates a carriage return). All examples of command lines are followed by a RETURN unless otherwise indicated.

About the Second Edition
Since this book was first published in 1990, it has become one of the most fundamental of the O'Reilly & Associates Nutshell Handbooks. Three important events occurred after it was written. The first was the publication of the POSIX standard for sea, and more importantly for awk. The second (perhaps due to the first) was the widespread availability of some version or other of new awk on all modern UNIX systems, both commercial ones and the freely available UNIX like systems such as NetBSD, FreeBSD, and Linux. The third was the source code availability of GNU sea, and three versions of awk, instead of just gawk.

For these and other reasons, O'Reilly & Associates decided that this handbook needed to be updated. The goals of the revision were to keep the flavor of the book intact ("if it ain't broke, don't fix it"), reorient the awk part of the book around POSIX awk, correct mistakes, and bring the book up to date.

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See All Sort by: Showing 1 – 20 of 40 Customer Reviews
  • Anonymous

    Posted June 25, 2012

    Barksripe

    "Thank you" the tabby warrior says as he heads towards the warriors den.

    1 out of 1 people found this review helpful.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    A border collie

    She raced in.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Sable

    But you stand here for a reason.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Hope

    "Do we look like them? I think I have two eyes. Not one."

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Jinx

    Yawneses.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Zach to hope

    Theres a cyclops ahead. Problaby 305 millinea old heading this way.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    To all!

    Move to 'borgias'! Asher is locked out!

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 5, 2014

    Asher

    "Pfff did you actually think I would keep you?" I blink innocently, "Aaaaanyway, make yourself at home. Or not. Idc" I shrug and walk over to the tables, sitting down and taking a gulp of my protein-enriched fruit smoothie

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 5, 2014

    The giant squid

    The giant squid flew off to the sign that says "WELCOME TO CAMP HALF BLOOD" And flew to her baby squids in the middle of the hill, "MY BABIES IVE MISSED YOU SO MUCH, IVE CAME ACROSS THE CAMPS AND WOODS TO GET TO YOU GUYS" as the baby squids roared at her mama happy with joy, the mama squid sat with her babies on the middle of the "welcome to camp half blood" sign hill, as they all roared loudly with joy.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Marlin

    He yawned and decided to call it a night. He went to the Apollo Cabin to get some sleep. ((Gtgtb bbt))

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  • Anonymous

    Posted July 5, 2014

    Red

    -.-

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  • Anonymous

    Posted July 6, 2014

    Um......

    Asher is locked out. Move to borgias sometime soon.

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  • Anonymous

    Posted July 6, 2014

    Leon

    He finished off the last cyclops, pulling a splinter from his arm, and sheathed his sword. He walked over to the group.p, staying in the shadows.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Herb

    He leaned against a nearby tree, calmly breathing. He tiredly twirled his dagger, the tip of the blade gently pushing into his left hand. <p>

    [Do we move now? And if so, someone needs to go post their post first, because my results are different and I don't know where main camp there is.]

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted July 6, 2014

    Sara TO ALL: PLEASE READ

    [Guys, Asher really is locked out. That's why he hasn't been posting. In fact, in another RP, he told me so...Move to 'borgias' result one for Main Camp. I've already posted there. Res two is bios, etc. Jasmine, someone else has posted the rules and landmarks for you. Now I have to make a cabin...which is always forgotten...-_-]

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  • Anonymous

    Posted July 5, 2014

    AnnaSophia

    (He just told me to tell y'all that.)

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  • Anonymous

    Posted July 5, 2014

    Heather

    "Um, I need to go to bed. Good night" she said, still with a grin on her face. She waved goodnight to him and everyone else, and started walking to her cabin.
    ((Gtgtb. Goodnight everyone!))

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted April 26, 2013

    Good Book

    Does what it says helps you learn sed and awk. Also helps you learn regualr expressioins

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted November 19, 2012

    Hello Maplestar

    Can i please join Treeclan
    My name is maplestream but if maplestar i can be oaktail and i want to be a med cat or med cat apprentice
    PLEASE answer
    Reply to maplestream
    P.S reply in mistystars omen

    0 out of 1 people found this review helpful.

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  • Anonymous

    Posted July 30, 2012

    Woodpasays screw this stupid clan i wil find abetter one

    Screw this stupid clan i will find a brtter onw

    0 out of 1 people found this review helpful.

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See All Sort by: Showing 1 – 20 of 40 Customer Reviews

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