《The AWK编程语言》深度指南：经典教材与实战解析

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《The AWK编程语言》是一本权威且实用的教程，由计算机科学领域的知名作者——Brian Kernighan和Peter Weinberger共同撰写。本书是学习AWK语言的首选资料，其特色在于作者深入浅出的讲解方式和丰富的实践环节，适合初学者和进阶者阅读。书中详尽地介绍了AWK这门强大的文本处理工具语言，它被广泛应用于数据处理、脚本编写和系统管理等领域。 AWK是一种专为处理文本数据而设计的编程语言，它结合了正则表达式和流程控制语句，使得在一行行的文本中进行复杂的数据筛选、转换和分析变得简单高效。其命名源于它的三个创建者名字的首字母：Aho、Weinberger和Kernighan。本书不仅涵盖了AWK的基本语法，如模式匹配、变量与数组、控制结构等核心概念，还通过实际案例帮助读者理解和掌握如何编写高效的工作流。《The AWK Programming Language》特别版（The AWK4 Programming Language）可能包含了对AWK语言的最新版本4的介绍，这部分内容可能会涉及更先进的特性以及优化的性能。书中还包括了练习题，读者可以通过这些题目来巩固所学知识并提升实践能力。该书由AT&T Bell Laboratories出版，体现了当时最先进的技术和实践环境，书中使用的工具和技术如Unix操作系统和Autologic APS-5光栅照排系统，反映了那个时代的技术背景。版权信息表明，这本书享有1988年的版权，并强调了其在图书馆分类中的位置，便于读者查找。《The AWK Programming Language》是一本不可或缺的参考书籍，无论你是初次接触AWK，还是希望进一步提升自己的AWK技能，它都能为你提供扎实的基础和深入的理解。对于IT专业人员来说，掌握这门语言将大大提高他们在处理大量文本数据时的效率和灵活性。

AN A

TUTORIAL

CHAPTER

$ awk

'$3

0 {

} ,

Beth

4.00

Beth

Dan

3.75

Dan

Kathy

3.75

Kathy

3.75

Kathy

The

heavy

characters

are

what the computer printed.

This behavior makes it easy to experiment with awk: type your program,

then type

data

it and see what happens. We again encourage you to try the

examples and variations on them.

Notice

that

the program

enclosed

single quotes on the command line.

This protects characters like $

the program from being interpreted by the

shell and also allows the program to be longer than one line.

This arrangement

convenient when the program

short (a

few

lines).

the program

long, however,

more convenient to put it into a separate file,

say

progfile,

and type the command line

awk

-f

progfile

optional list

input files

The

-f

option instructs awk to fetch the program from the named file. Any

filename can be used

place

progfile.

Errors

you make an error

an awk program, awk will give you a diagnostic

message. For example, if you mistype a brace, like this:

awk

'$3

0 [

emp.data

you will get a message like this:

awk:

syntax

error

source

line

context

>>>

[ <<<

extra

}

missing

awk:

bailing

out

source

line

"Syntax error" means

that

you have made a grammatical error that was

detected

the place marked

>>>

<<<.

"Bailing

out"

means

that

recovery was attempted. Sometimes

you

get a little more help about what the

error was, such as a report

mismatched braces or parentheses.

Because

the syntax error, awk did not try to execute this program. Some

errors, however, may not be detected until your program

running. For exam-

ple, if you attempt to divide a number

zero, awk will stop its processing and

report the input line number and the line number

the program

which the

division was attempted.

SECTION

1.2

SIMPLE OUTPUT 5

1.2 Simple Output

The

rest

this chapter contains a collection

short, typical awk programs

based on manipulation

the emp o

data

file above. We'll explain briefly

what's going on, but these examples are meant mainly to suggest useful opera-

tions

that

are

easy to do with awk - printing fields, selecting input, and

transforming data. We

are

not showing everything

that

awk

can

do by any

means, nor

are

going into many details about the specific things presented

here. But by the end

this chapter, you will be able to accomplish quite a bit,

and you'll find it much easier to read the later chapters.

will usually show just the program, not the whole command line. In

every case, the program can be run either by enclosing it in quotes as the first

argument

the

awk

command, as shown above, or by putting it

a file and

invoking awk on

that

file with the

-f

option.

There

are

only two types

data

in awk: numbers and strings

characters.

The emp 0

data

file

typical

this kind of information - a mixture

words

and numbers separated

blanks

and/or

tabs.

Awk reads its input one line

a time and splits each line into fields, where,

default, a field

a sequence

characters

that

doesn't contain any blanks or

tabs. The first field

the current input line

called

$1,

the second

$2,

and

forth.

The

entire line

called $0. The number

fields can vary from line to

line.

Often, all we need to do

print some or all

the fields

each line,

perhaps performing some calculations. The programs

this section

are

all of

that

form.

Printing Every Line

action has

pattern, the action

performed for all input lines. The

statement

by itself prints the current input line, so the program

{

}

prints all

its input on the standard output. Since

the whole line,

{

}

does the same thing.

Printing Certain Fields

More than one item can be printed on the same output line with a single

statement. The program to print the first and third fields

each input

line

{

$1,

}

With

emp.

data

as input, it produces

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