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.

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Table of Contents (11 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Get in touch
Free Chapter
1
Getting Started with AWK Programming
Getting Started with AWK Programming
AWK programming language overview
Getting started with AWK
AWK standard options
Summary
2
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
3
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
4
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
5
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
6
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
7
AWK Control Flow Statements
AWK Control Flow Statements
Conditional statements
Looping statement
Statements affecting flow control
Summary
8
AWK Functions
AWK Functions
Built-in functions
User-defined functions
Summary
9
GNU's Implementation of AWK – GAWK (GNU AWK)
GNU's Implementation of AWK – GAWK (GNU AWK)
Things you don't know about GAWK
Summary
10
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

Redirecting output to file

Till now we have been sending the output of print and printf commands to stdout, that is, the screen. However, we can also redirect the output to files by using the redirection operator. Redirection is done after the print command. It is the same as we do in shell commands using redirection operator.

There are three forms of output redirection:

  • Output to file
  • Output appended to a file
  • Output through a pipe to another command

Redirecting output to a file (>)

This redirection operator (>) prints the items into the output file. Its syntax is as follows:

print items > demo

In this type of redirection, if the output file named demo exists, then it is erased before the first output is written...

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