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Learning AWK Programming

By : Kalkhanda

5 (4)

Learning AWK Programming

5 (4)

By: 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

Preface

Who this book is for

What this book covers

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Getting Started with AWK Programming

Getting Started with AWK Programming

AWK programming language overview

Getting started with AWK

AWK standard options

Summary

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

Summary

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

Summary

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

Summary

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

Summary

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

Summary

AWK Control Flow Statements

AWK Control Flow Statements

Conditional statements

Looping statement

Statements affecting flow control

Summary

AWK Functions

AWK Functions

Built-in functions

User-defined functions

Summary

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

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

Things you don't know about GAWK

Summary

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

Summary

Further reading

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Case-sensitive matching

In bracket expressions, we can use both lowercase and uppercase characters to match the characters for case-insensitive results, but the same is not true for other regular expressions. However, this becomes difficult if you have to match to many characters. Here comes the two built-in string functions of AWK, tolower() and toupper(). Using these two functions, we can perform case-insensitive match operations.

For example, to match the first name 'John' of an employee in the emp.dat file, we can perform a case-insensitive match using the tolower() function, as follows:

$ awk 'tolower($1) ~ /john/' emp.dat

The output on execution of this code is as follows:

John    Kapur   9911556789  [email protected]      M   hr      2200

Another way to perform a case-insensitive match operation is by setting the IGNORECASE bash variable value to TRUE.

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