Book Image

Linux Command Line and Shell Scripting Bible - Third Edition

By : Richard Blum, Christine Bresnahan
Book Image

Linux Command Line and Shell Scripting Bible - Third Edition

By: Richard Blum, Christine Bresnahan

Overview of this book

The Linux command line enables you to type specific shell commands directly into the system to manipulate files and query system resources. Command line statements can be combined into short programs called shell scripts, a practice increasing in popularity due to its usefulness in automation. Linux is a robust system with tremendous potential, and Linux Command Line and Shell Scripting Bible opens the door to new possibilities. Linux Command Line and Shell Scripting Bible is your essential Linux guide. It contains new functional examples that are fully updated to align with the latest Linux features. Beginning with command line fundamentals, the book moves into shell scripting and shows you the practical application of commands in automating frequently performed functions. This book is a complete guide providing detailed instruction and expert advice working within this aspect of Linux. Whether used as a tutorial or as a quick reference, this book contains information that every Linux user should know.
Table of Contents (34 chapters)
Part I: The Linux Command Line
Part II: Shell Scripting Basics
Part III: Advanced Shell Scripting
Part IV: Creating Practical Scripts
End User License Agreement

Using Patterns

The gawk program supports several types of matching patterns to filter data records, in much the same way as the sed editor. Chapter 19 showed two special patterns in action. The BEGIN and END keywords are special patterns that execute statements before or after the data stream data has been read. Similarly, you can create other patterns to execute statements when matching data appears in the data stream.

This section demonstrates how to use matching patterns in your gawk scripts to limit what records a program script applies to.

Regular expressions

Chapter 20 showed how to use regular expressions as matching patterns. You can use either a Basic Regular Expression (BRE) or an Extended Regular Expression (ERE) to filter which lines in the data stream the program script applies to.

When using a regular expression, the regular expression must appear before the left brace of the program script that it controls:

$ gawk 'BEGIN{FS=","} /11/{print $1}' data1...