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

Changing the Flow

Normally, the sed editor processes commands starting at the top and proceeding toward the end of the script (the exception is the D command, which forces the sed editor to return to the top of the script without reading a new line of text). The sed editor provides a method for altering the flow of the command script, producing a result similar to that of a structured programming environment.


In the previous section, you saw how the exclamation mark command is used to negate the effect of a command on a line of text. The sed editor provides a way to negate an entire section of commands, based on an address, an address pattern, or an address range. This allows you to perform a group of commands only on a specific subset within the data stream.

Here's the format of the branch command:

[address]b [label]

The address parameter determines which line or lines of data trigger the branch command. The label parameter defines the location to branch to. If the label...