Linux Fundamentals - Part 9: Bash Scripting (Arrays)

Bash Arrays

A Bash array is a variable that can hold multiple values, each stored at a specific index. Instead of creating many separate variables, arrays let us group related data together.

Example use cases:

• List of servers
• Packages to install
• Users to create
• Files or directories to process

Creating an Array

Basic Array Syntax

servers=("web1" "web2" "web")

Each value is separated by a space and wrapped in parentheses.

You can also create arrays like this:

servers[1]="web1"
servers[2]="web2"
servers[3]="web3"

Accessing Array Elements

To access an element, use its index:

echo ${servers[0]}

Output:

web1

Always use ${} when accessing array values.

Accessing All Elements

To print all elements in an array:

echo ${servers[@]}

Or Loop through them:

for server in "${servers[@]}"; do
    echo "Server: $servers"
done

Output:

Server: web1
Server: web2
Server: web3

Getting the Array Length

Knowing how many items are in an array is crucial for automation.

echo ${#servers[@]}

Adding # before variable_name which is servers.
This prints the number of elements in the array.

Output:

3

Adding Elements to an Array

You can append new values like this:

servers+=("asd1")

Now the array contains:

web1 web2 web3 asd1

Removing Elements from an Array

Use unset to remove a specific index:

unset servers[1]

This removes the value but does not reindex the array automatically.

To see Indexes:

echo ${!servers[@]}

Output:

0 2 3

Looping with Indexes (Platform Engineer Pattern)

Sometimes you need both the index and the value:

#!/bin/bash

servers=( "web1" "web2" "web3" "asd1" )

for i in "${!servers[@]}"; do
  echo "Index $i → ${servers[$i]}"
done

Output:

Index 0 -> web1
Index 1 -> web2
Index 2 -> web3
Index 3 -> asd1

To Review

Arrays + Functions (Very Important)

Platform engineers often combine functions and arrays.

#!/bin/bash
# Script: arrays_functions.sh
# Purpose: Demonstrate how to use Bash arrays inside functions

# Define a function to print package installation messages
print_packages() {
  for pkg in "$@"; do
    echo "Installing $pkg..."
  done
}

# Create an array of packages
packages=("nginx" "docker" "git")

# Call the function and pass all array elements
print_packages "${packages[@]}"

# Bonus: Add a new package and call the function again
packages+=("htop")
echo ""
echo "After adding a new package:"
print_packages "${packages[@]}"

How It Works

packages=("nginx" "docker" "git") - creates an array of package names.
print_packages() - a function that loops through all arguments ($@) and prints a message.
print_packages "${packages[@]}" - passes all array elements to the function.
packages+=("htop") - appends a new package to the array.
Calling print_packages again shows the updated array.

Expected Output:

Installing nginx...
Installing docker...
Installing git...

After adding a new package:
Installing nginx...
Installing docker...
Installing git...
Installing htop...

Today, I learned about Bash arrays and how they can store multiple values in a single variable, which makes scripts more organized. I also explored using arrays with functions, but I’m having a hard time understanding how $@ passes array elements to a function. I practiced looping through the array inside a function, but I still feel a bit unsure about combining arrays and functions in my scripts. This lesson showed me that I need more practice to fully understand this important concept for automation tasks.

Tomorrow, I will review and practice Bash arrays to become more comfortable using them. I also plan to explore more ways arrays are used in real automation tasks, so I can get closer to being platform engineer ready.