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 Special Parameter Variables

A few special bash shell variables track command line parameters. This section describes what they are and how to use them.

Counting parameters

As you saw in the last section, you should verify command line parameters before using them in your script. For scripts that use multiple command line parameters, this checking can get tedious.

Instead of testing each parameter, you can count how many parameters were entered on the command line. The bash shell provides a special variable for this purpose.

The special $# variable contains the number of command line parameters included when the script was run. You can use this special variable anywhere in the script, just like a normal variable:

$ cat
# getting the number of parameters
echo There were $# parameters supplied.
$ ./
There were 0 parameters supplied.
$ ./ 1 2 3 4 5
There were 5 parameters supplied.
$ ./ 1 2 3 4 5 6 7 8 9 10
There were 10 parameters...