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 Working with shell scripts

 Doing arithmetic in shell scripts

 Running loops and cases in shell scripts

 Creating simple shell scripts

You'd never get any work done if you typed every command that needs to be run on your Linux system when it starts. Likewise, you could work more efficiently if you grouped together sets of commands that you run all the time. Shell scripts can handle these tasks.

A shell script is a group of commands, functions, variables, or just about anything else you can use from a shell. These items are typed into a plain-text file. That file can then be run as a command. Linux systems have traditionally used system initialization shell scripts during system startup to run commands needed to get services going. You can create your own shell scripts to automate the tasks that you need to do regularly.

For decades, building shell scripts was the primary skill needed to join together sets of tasks in UNIX and Linux systems. As demands for configuring Linux systems grew beyond single-system setups to complex, automated cluster configurations, more structured methods have arisen. These methods include Ansible playbooks and Kubernetes YAML files, described later in cloud-related chapters. That said, writing shell scripts is still the best next step from running individual commands to building repeatable tasks in Linux systems.

This chapter provides a rudimentary overview of the inner workings of shell scripts and how they can be used. You learn how simple scripts can be harnessed to a scheduling facility (such as cron or at) to simplify administrative tasks or just run on demand as they are needed.