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 evaluation order and precedence in decreasing relevance

Operators are evaluated in a precise order and we must keep this in mind when working with them. It is not so easy to remember what is evaluated before and what after, so the following table will help us to keep in mind the order and precedence of operators:

Operator

Evaluation order

++ --

Unary operators for incrementing/decrementing, evaluated from left to right

+- !~

Unary plus and minus, evaluated from right to left

* / %

Multiplication, division, modulo, are evaluated from left to right and are evaluated after

+ -

Addition and subtraction are evaluated from left to right

<<>>

Bitwise shift are evaluated from left to right

<= =><>

Comparison operators, from left to right

== !=

Equality operators, from left to right

&

Bitwise AND...