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

Negating a Command

Chapter 19 showed that the sed editor applies commands either to every text line in the data stream or to lines specifically indicated by either a single address or an address range. You can also configure a command to not apply to a specific address or address range in the data stream.

The exclamation mark command (!) is used to negate a command. This means in situations where the command would normally have been activated, it isn't. Here's an example demonstrating this feature:

$ sed -n '/header/!p' data2.txt
This is the first data line.
This is the second data line.
This is the last line.

The normal p command would have printed only the line in the data2 file that contained the word header. By adding the exclamation mark, the opposite happens — all lines in the file are printed except the one that contained the word header.

Using the exclamation mark comes in handy in several applications. Recall that earlier in the chapter, the “...