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

Being Shifty

Another tool you have in your bash shell tool belt is the shift command. The bash shell provides the shift command to help you manipulate command line parameters. The shift command literally shifts the command line parameters in their relative positions.

When you use the shift command, it moves each parameter variable one position to the left by default. Thus, the value for variable $3 is moved to $2, the value for variable $2 is moved to $1, and the value for variable $1 is discarded (note that the value for variable $0, the program name, remains unchanged).

This is another great way to iterate through command line parameters, especially if you don't know how many parameters are available. You can just operate on the first parameter, shift the parameters over, and then operate on the first parameter again.

Here's a short demonstration of how this works:

$ cat
# demonstrating the shift command
while [ -n "$1" ]