Bash Scripting — Manipulating Arrays

Welcome to Chapter 21 — Manipulating Arrays 🎉

Arrays are one of the most powerful features in Bash scripting. Whether you’re managing a list of servers, processing log entries, or building a configuration tool — arrays keep your data organised and your scripts clean.

In this chapter, we’ll go from the basics of creating and reading arrays all the way through to sorting, slicing, and understanding when arrays beat plain strings.

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What You’ll Learn

#	Topic	What’s Covered
1	Indexed Array CRUD	Create, read, update, delete elements in indexed arrays
2	Associative Array CRUD	Key-value pairs with declare -A, iteration, existence checks
3	Array Slicing and Copying	Sub-arrays, appending, deduplication, array ↔ string
4	Sorting Arrays	mapfile + sort, numeric sort, reverse, sort by field
5	Array vs String Performance	When to reach for arrays, word-splitting traps, nameref passing
6	Practice Exercises	5 hands-on challenges from easy to advanced

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Prerequisites

Before diving in, make sure you’re comfortable with:

• Basic Bash syntax (variables, quoting, loops)
• Running scripts from the terminal
• The difference between $var and "$var" (quoting matters!)

If you need a refresher, revisit the earlier chapters on variables and loops.

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Indexed vs Associative Arrays — Quick Overview

Bash supports two kinds of arrays:

Indexed Arrays

Elements are stored by numeric position (starting at 0).

fruits=("apple" "banana" "cherry")
echo "${fruits[1]}"   # banana

Associative Arrays

Elements are stored by string keys (like a dictionary or hash map). You must declare them with declare -A.

declare -A colours
colours[sky]="blue"
colours[grass]="green"
echo "${colours[sky]}"   # blue

Key Differences at a Glance

Feature	Indexed	Associative
Declaration	arr=() or declare -a	declare -A
Keys	Integers (0, 1, 2…)	Arbitrary strings
Order	Insertion order preserved	No guaranteed order
Bash version	3.0+	4.0+

💡 Tip: Run bash --version to check. Most modern Linux distros ship with Bash 5.x. macOS ships with Bash 3.2 by default — install a newer version via Homebrew if you need associative arrays.

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How This Chapter Is Organised

Each lesson follows a consistent pattern:

1. Concept — a short explanation with a diagram or table
2. Script — a complete, runnable example with #!/usr/bin/env bash and set -euo pipefail
3. Expected output — so you can verify your results
4. Mini-exercise — a quick challenge to reinforce the concept

The final lesson is a dedicated set of practice exercises that tie everything together.

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Let’s Get Started!

Head over to Indexed Array CRUD to begin working with arrays right away.

Happy scripting! 🚀