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)

Operators

What we have looked at so far is tinkering with values returned from variable expansions and descriptors used in a tricky way. So, something nice, but we could not do much more, since we do not have a way to actually relate values, compare or even modify at our will.

Here is where the operators come in to play, and we will see how to modify the value of a variable so that it will hold a value and, over time, modify to gather new information. So, let's start from something simple, from basic math then move on to something more complex.

One last thing we have to bear in mind before proceeding is that the operators follow an order of precedence:

  • The compound logical operators -a, -o, and && have a low precedence
  • The arithmetic operators have the following precedence:
    • Multiply
    • Divide
    • Add
    • Subtract
  • The evaluation of operators with equal precedence is from...