Book Image

Mastering Bash

By : Giorgio Zarrelli
Book Image

Mastering Bash

By: Giorgio Zarrelli

Overview of this book

System administration is an everyday effort that involves a lot of tedious tasks, and devious pits. Knowing your environment is the key to unleashing the most powerful solution that will make your life easy as an administrator, and show you the path to new heights. Bash is your Swiss army knife to set up your working or home environment as you want, when you want. This book will enable you to customize your system step by step, making your own real, virtual, home out of it. The journey will take you swiftly through the basis of the shell programming in Bash to more interesting and challenging tasks. You will be introduced to one of the most famous open source monitoring systems—Nagios, and write complex programs with it in any languages. You’ll see how to perform checks on your sites and applications. Moving on, you’ll discover how to write your own daemons so you can create your services and take advantage of inter-process communication to let your scripts talk to each other. So, despite these being everyday tasks, you’ll have a lot of fun on the way. By the end of the book, you will have gained advanced knowledge of Bash that will help you automate routine tasks and manage your systems.
Table of Contents (15 chapters)

Logical operators

Here, we come to something really useful for our scripts, a bunch of operators that will enable us to perform some tests and react as a consequence. So, we will be able to make our script react to a some change or user input and be more flexible. Let's see what is available.

Logical NOT (!)

The NOT operator is used to test whether an expression is true and holds true when the expression is false:

[! expression ]  

Let's go back to one of our previous scripts and make it more user-friendly:

#!/bin/bash    
echo "Hello user, please give me a number between 10 and 12: "
read user_input
if [ ! ${user_input} -eq11 ]
then
echo "The number ${user_input} is not what we are looking for...