Book Image

Learning AWK Programming

By : Shiwang Kalkhanda

5 (1)

Book Image

Learning AWK Programming

5 (1)

By: Shiwang Kalkhanda

Overview of this book

AWK is one of the most primitive and powerful utilities which exists in all Unix and Unix-like distributions. It is used as a command-line utility when performing a basic text-processing operation, and as programming language when dealing with complex text-processing and mining tasks. With this book, you will have the required expertise to practice advanced AWK programming in real-life examples. The book starts off with an introduction to AWK essentials. You will then be introduced to regular expressions, AWK variables and constants, arrays and AWK functions and more. The book then delves deeper into more complex tasks, such as printing formatted output in AWK, control flow statements, GNU's implementation of AWK covering the advanced features of GNU AWK, such as network communication, debugging, and inter-process communication in the GAWK programming language which is not easily possible with AWK. By the end of this book, the reader will have worked on the practical implementation of text processing and pattern matching using AWK to perform routine tasks.

Preface

Who this book is for

What this book covers

To get the most out of this book

Free Chapter

Getting Started with AWK Programming

Getting Started with AWK Programming

AWK programming language overview

Getting started with AWK

AWK standard options

Working with Regular Expressions

Working with Regular Expressions

Introduction to regular expressions

Basic regular expression construct

Understanding regular expression metacharacters

Precedence in regular expressions

GAWK-specific regular expression operators

Case-sensitive matching

Escape sequences

AWK Variables and Constants

AWK Variables and Constants

Built-in variables in AWK

Environment variables in AWK

Environment variables in GAWK

String constants

Numeric constants

Conversion between strings and numbers

Working with Arrays in AWK

Working with Arrays in AWK

One-dimensional arrays

Assignment in arrays

Accessing elements in arrays

Referring to members in arrays

Processing arrays using loops

Using the split() function to create arrays

Delete operation in arrays

Multidimensional arrays

Printing Output in AWK

Printing Output in AWK

The print statement

Role of output separator in print statement

Pretty printing with the printf statement

Escape sequences for special character printing

Different format control characters in the format specifier

Format specification modifiers

Redirecting output to file

AWK Expressions

AWK Expressions

AWK variables and constants

Arithmetic expressions using binary operators

Assignment expressions

Increment and decrement expressions

Relational expressions

Logical or Boolean expressions

Ternary expressions

Unary expressions

Exponential expressions

String concatenation

Regular expression operators

Operators' Precedence

AWK Control Flow Statements

AWK Control Flow Statements

Conditional statements

Looping statement

Statements affecting flow control

AWK Functions

Built-in functions

User-defined functions

GNU's Implementation of AWK – GAWK (GNU AWK)

GNU's Implementation of AWK – GAWK (GNU AWK)

Things you don't know about GAWK

Practical Implementation of AWK

Practical Implementation of AWK

Working with one-liners for text processing and pattern matching with AWK

Use case examples of pattern matching using AWK

Further reading

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Escape sequences

When using regular expressions and strings, certain characters cannot be included literally in string constants ("hello") or regular expression constants (/hello/). To specify the characters for which there may not be other notations, they are represented as escape sequences. Escape sequences begin with a backslash ('\'). For example, it can represent that an \n newline character is used, which otherwise cannot be represented in strings or regular expressions. Similarly, \b stands for backspace, \t stands for tab, and \/ represents a forward slash. They are quite useful in generating formatted output.

For example, to insert a new line after each line of the emp.dat file, we can use the \n escape sequence, as follows:

$ awk '{ print $0"\n" }' emp.dat

The output on execution of the given code is as follows:

Jack    Singh ...