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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Preface

This book is for anyone who is inclined to learn text processing and data extraction in a Unix-like environment. Readers will gain sufficient practical knowledge to write AWK one-liners for extracting data and write clean and small AWK programs to solve complex problems. You will be able to automate the process of cleaning any raw data, remove any extra unnecessary stuff, and create a desired reportable output. Examples given in the book are easily reproducible and will help you better understand AWK.

Text processing is used in data mining, data cleaning of CSV, and other similar-format database files. System administrators use it in their shell scripts to automate tasks and filter out command output. It is used extensively with grep, egrep, fgrep, and regular expressions for parsing text files. Its use cases vary from industry to industry, such as telecom enterprises and business process organizations that deal with large CSV files for storing logs and other user information. They use AWK for cleaning and transforming the structure of data from one form to another.

AWK one of the oldest and most powerful utilities that exists in all and Linux distributions. It is used as a command-line utility for performing basic text processing operations and as a programming language when dealing with complex text processing. The best thing about AWK is that it is a data-driven language: you describe the data you wish to work with, and the set of actions you want to perform in the case of a pattern match. This book will provide you with a rundown, explaining the concepts to help you get started with AWK. We will cover every element of functions, variables, and more.

This book will enable the user to perform text filtering, text cleaning, and parsing of input in user-defined formats to create elegant reports. Our main focus throughout the book is on learning AWK with examples and small scripts to quickly solve user problems. The mission of this book is to make the reader comfortable and friendly with AWK.