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)

Pipes

We can describe a pipeline as a sequence of processes tied together by stdout and stdin so that the output of one process becomes the input of the following one. This is a simple form of IPC, commonly known as anonymous pipe, and it is a one-way form of communicating: whatever comes from standard output of the preceding process flows into the standard input of the following one; nothing comes back from the latter to the former.

Let's see an example that will clarify the concept of anonymous pipe, staring with a simple ps command:

zarrelli:~$ ps 
PID TTY TIME CMD
1427 pts/0 00:00:00 bash
12112 pts/0 00:00:00 ps

We have a simple listing with some commands: PID, TTY, and CMD. Let's say we want to trim down the output to just PID and CMD. We could alter the output using some ps switches, but who remembers them? It's easier to use something that is capable of mangling...