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)
2
Part I: The Linux Command Line
13
Part II: Shell Scripting Basics
20
Part III: Advanced Shell Scripting
28
Part IV: Creating Practical Scripts
32
End User License Agreement

Learning about Variable Arrays

A really cool feature of environment variables is that they can be used as arrays. An array is a variable that can hold multiple values. Values can be referenced either individually or as a whole for the entire array.

To set multiple values for an environment variable, just list them in parentheses, with values separated by spaces:

$ mytest=(one two three four five)
$

Not much excitement there. If you try to display the array as a normal environment variable, you'll be disappointed:

$ echo $mytest
one
$

Only the first value in the array appears. To reference an individual array element, you must use a numerical index value, which represents its place in the array. The numeric value is enclosed in square brackets:

$ echo ${mytest[2]}
three
$

To display an entire array variable, you use the asterisk wildcard character as the index value:

$ echo ${mytest[*]...