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)

What is a subshell?

Let's start with a more basic question. What is a shell? To make it simple, a shell is an interface between the user and the underlying operating system. It can be a command-line interpreter or a graphic interface, but the purpose of a shell is to be an intermediary between the user and the core of the system, allowing the former to access the services offered by the latter. So, for instance, a bash shell gives us a command-line interface access through a Terminal and a series of commands that allows us to communicate with the operating system and make use of its services to perform tasks.

In a shell, each command is usually executed after the former has concluded its task, but we can change to some extent this behavior leveraging some key concepts: background process, signals, and subshells.