Shell Scripting: basic concepts

Consider a scenario: setting up a new development environment. This typically involves creating a user, a group, directories, and files, and installing and running software. These commands would have to be run manually in the terminal.

Manually running each of these commands can be time-consuming and prone to errors. Shell scripting offers an efficient solution by allowing you to automate these tasks through scripts.

This article introduces shell scripting, focusing on practical applications in DevOps.

What is a Shell?

A shell is a program that interprets and executes commands entered by a user in a terminal.

When you type commands in your terminal, the shell translates them into something the computer understands.

Why is a file with commands called a shell script?

A shell script is a text file that contains a sequence of commands you would typically enter in your terminal. When you execute this file, the shell processes and runs each command in order, just as if you had typed them manually. This allows for task automation.

Common Shells:

• Sh: (bourne SHell) An older shell that Bash is derived from.

• Bash: (bourne Again SHell) a superset of sh with a more elegant syntax and more functionality.The most widely used shell today.

• Zsh: Known for its extensive customization options, another popular shell.

Creating a Shell Script

To automate the above tasks, create a shell script in your home directory or a dedicated project directory.

• Create and edit the file vim setup.sh

• Add the shebang line on the first line: #!/bin/bash

• Paste the commands into the script:

• 

  Switch to command mode, save and exit this file :wq

• Execute the script ./setup.sh

Bash is a powerful tool that lets you write scripts to automate tasks. It can do much more than just running simple commands. You can use it to create complex programs with features like variables, loops, and conditionals.

While Bash is great for many automation tasks, other tools like Python programming language or Ansible might be better suited for specific jobs.

Common uses for Bash scripts include:

• Routine tasks like file backups

• Network monitoring, host scanning, and port checking

• Server configuration tasks such as installing new software, creating users, or interacting with external services and APIs

Practical Applications

Shell scripts are useful for automating DevOps tasks, improving efficiency, and creating reusable documentation. By bundling commands into scripts, you can optimize repetitive processes, reduce errors, and easily share and reproduce setups across different environments.

Common applications include:

• Server Configuration: Install software, create users, and configure services.

• File Management: Create, copy, move, and delete files and directories.

• User Management: Add, remove, and modify user accounts.

• Backup and Restoration: Automate regular backups and restore data.

• Monitoring: Check system resources, network connectivity, and service status.

• Deployment: Deploy applications and configurations to servers.

Shell scripting is a powerful tool for automating repetitive tasks, improving efficiency, and reducing errors. By incorporating error handling, you can create more reliable and robust scripts.

Learning More:

Here are some resources to learn more about shell scripting:

Bash: https://opensource.com/resources/what-bash

Zsh: https://opensource.com/article/19/9/getting-started-zsh

Sh: https://opensource.com/article/17/1/getting-started-shell-scripting