Book Image

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

By : Sebastiaan Tammer
Book Image

Learn Linux Shell Scripting – Fundamentals of Bash 4.4

By: Sebastiaan Tammer

Overview of this book

Shell scripts allow us to program commands in chains and have the system execute them as a scripted event, just like batch files. This book will start with an overview of Linux and Bash shell scripting, and then quickly deep dive into helping you set up your local environment, before introducing you to tools that are used to write shell scripts. The next set of chapters will focus on helping you understand Linux under the hood and what Bash provides the user. Soon, you will have embarked on your journey along the command line. You will now begin writing actual scripts instead of commands, and will be introduced to practical applications for scripts. The final set of chapters will deep dive into the more advanced topics in shell scripting. These advanced topics will take you from simple scripts to reusable, valuable programs that exist in the real world. The final chapter will leave you with some handy tips and tricks and, as regards the most frequently used commands, a cheat sheet containing the most interesting flags and options will also be provided. After completing this book, you should feel confident about starting your own shell scripting projects, no matter how simple or complex the task previously seemed. We aim to teach you how to script and what to consider, to complement the clear-cut patterns that you can use in your daily scripting challenges.
Table of Contents (24 chapters)
Title Page
About Packt
Contributors
Preface
Free Chapter
1
Introduction
Index

Summary


We started this chapter by showing the new at command and explaining how we can use at for scheduling scripts. We described the timestamp syntax for at and how it contains a queue for all scheduled jobs. We explained how at is mostly used for ad hoc scheduled commands and scripts, before we continued to the more powerful cron scheduler.

The cron daemon, responsible for most scheduled tasks on a system, is a very powerful and flexible scheduler, which is most often used via the so-called crontab. This is a user-bound file, which contains instructions for cron on when and how to run commands and scripts. We presented the timestamp syntax that is used in a crontab.

The second part of the chapter dealt with logging our scheduled commands and scripts. When a command is run interactively on the command line, there is no need for dedicated logging, but scheduled commands are not interactive, and thus need additional mechanisms. Output from scheduled commands can either be mailed to a local...