Understanding Shell Scripting

Shell scripting is a powerful way to automate repetitive tasks, manage system processes, and handle system administration tasks in a Linux environment. By writing simple scripts, you can significantly improve productivity and reduce errors. This blog will introduce you to shell scripting basics, followed by examples of real-world tasks using scripts to install packages and create backups.

Example 1: Installing Nginx

Here’s a script that installs the popular web server Nginx:

#!/bin/bash

<<note
This script will install nginx
note

echo "*************INSTALLING NGINX*************"

sudo apt-get update
sudo apt-get install nginx -y

sudo systemctl start nginx
sudo systemctl enable nginx

echo "*************INSTALLED NGINX*************"        

Explanation

1. Documentation: The <<note and note block provides a multi-line comment describing the script’s purpose.
2. Updating the Package List:sudo apt-get update ensures the package list is up to date before installation.
3. Installing Nginx:sudo apt-get install nginx -y installs Nginx, where -y automatically confirms the installation prompt.
4. Starting and Enabling Nginx:

- sudo systemctl start nginx starts the web server immediately.

- sudo systemctl enable nginx ensures Nginx starts automatically on system boot.

Example 2: Installing Any Package

Sometimes, you might want a generic script to install any package by simply passing its name as an argument.

#!/bin/bash

<<note
This Script will install any package passed as argument
note

echo "**********INSTALLING $1**********"

sudo apt-get update
sudo apt-get install $1 -y

sudo systemctl start $1
sudo systemctl enable $1

echo "**********INSTALLED $1**********"        

Explanation

1. Dynamic Package Name: $1 is a parameter, which means it takes the value of the first argument passed to the script. For example, running ./install.sh apache2 will replace $1 with apache2.
2. Modularity: This script is versatile and reusable for any package. Simply change the argument to install a different package.
3. Example Usage:

./install.sh apache2  # Installs Apache2
./install.sh mysql    # Installs MySQL        

4. Starting and Enabling the Package:After installation, the script attempts to start and enable the service.

Example 3: Creating Backups

Backups are essential for safeguarding data. The following script creates a compressed backup of any directory.

#!/bin/bash

<<note
This script takes backup of any destination path given in argument

./backup.sh /home/ubuntu/scripts
note

function create_backup() {
timestamp=$(date '+%Y-%m-%d_%H-%M-%S')

backup_dir="/home/ubuntu/backups/${timestamp}_backup.zip"

zip -r $backup_dir $1

echo "BACKUP COMPLETE"
}

create_backup $1
        

Explanation

1. Timestamped Backups: The script generates a unique timestamp using date '+%Y-%m-%d_%H-%M-%S', ensuring every backup file has a unique name.
2. Backup Directory: The backup is saved in /home/ubuntu/backups/. The output file is a .zip archive named with the timestamp.
3. Zipping Files: zip -r $backup_dir $1 recursively compresses the specified directory into a zip file.
4. Functionality: The create_backup function encapsulates the backup logic, making the script modular and easy to maintain.
5. Dynamic Backup Path: $1 is used to accept the target directory as an argument.

./backup.sh /home/ubuntu/scripts