Arrays

Arrays in Bash empower you to store multiple values in an indexed collection, offering direct access to any element—first, middle, or last—by its index. This is analogous to reaching into a specific drawer when you know exactly where your socks are kept, rather than inspecting each one sequentially.

The image illustrates the concept of arrays using a drawer analogy, showing three drawers labeled 1, 2, and 3 on the left, and an array with indices 0, 1, and 2 on the right.

Bash arrays are zero-indexed: the first element is at index 0, the second at 1, and so on.

Why Use Arrays?

Direct element access reduces loops and conditional checks.
Cleaner scripts when handling lists of servers, filenames, or configurations.
Improved performance versus string-based lists requiring manual parsing.

Compare a string-based iteration:

#!/usr/bin/env bash

servers="server1 server2 server3"
for server in ${servers}; do
  if [[ "$server" == "server2" ]]; then
    server="${server}.kodekloud.com"
  fi
  echo "$server"
done

Output:

server1
server2.kodekloud.com
server3

This checks every item, akin to opening each drawer until you find your socks. Arrays eliminate that overhead.

Declaring Arrays

1. Assigning by Index

#!/usr/bin/env bash

course_sections[0]="Introduction"
course_sections[1]="Coding Standards"
course_sections[2]="Refresher"

echo "${course_sections[0]}"   # Introduction
echo "${course_sections[1]}"   # Coding Standards
echo "${course_sections[2]}"   # Refresher

The image illustrates an array with three indexed elements (0, 1, 2), highlighting the second element (index 1) as "server[1]".

2. Inline Initialization

#!/usr/bin/env bash

declare -a course_sections=("Introduction" "Coding Standards" "Refresher")
echo "${course_sections[@]}"   # Introduction Coding Standards Refresher

You can also omit declare -a:

course_sections=("Intro" "Middle" "End")

Accessing Array Elements

Operation	Syntax	Example Output
Single element	`${array[index]}`	`${course_sections[1]}` → Coding Standards
All elements	`${array[@]}`	`${course_sections[@]}` → all items
Number of elements	`${#array[@]}`	count of items
All indices (keys)	`${!array[@]}`	list of valid indices
Slice	`${array[@]:start:length}`	subset of elements

Get All Elements

#!/usr/bin/env bash

sections=("Intro" "Body" "Conclusion")
echo "${sections[@]}"  # Intro Body Conclusion

Quoting Arrays: Preserve Whitespace

Unquoted expansions split on spaces:

#!/usr/bin/env bash

sections=("Coding Standards" "Best Practices")

# Unquoted
for s in ${sections[@]}; do
  echo "$s"
done

# Quoted
for s in "${sections[@]}"; do
  echo "$s"
done

Output:

Coding
Standards

Coding Standards

Always quote ${array[@]} in loops or commands to preserve elements containing spaces.
Unquoted expansions can lead to unexpected word splitting.

Modifying Arrays

Append an Element

#!/usr/bin/env bash

sections=("Intro" "Methods")
sections+=("Conclusion")
echo "${sections[@]}"  # Intro Methods Conclusion

Overwrite Entire Array

Assigning a string replaces index 0 but retains the array type:

#!/usr/bin/env bash

sections=("A" "B" "C")
sections="NewSection"
echo "${sections[@]}"  # NewSection

Introduction

Conventions

Refresher

Streams

Expansions - Part One

Globs

Expansions - Part Two

Special Shell Variables

Good Practices applied

awk

sed

Arrays

Why Use Arrays?

Declaring Arrays

1. Assigning by Index

2. Inline Initialization

Accessing Array Elements

Get All Elements

Quoting Arrays: Preserve Whitespace

Modifying Arrays

Append an Element

Overwrite Entire Array

Further Reading and References

Watch Video

​Why Use Arrays?

​Declaring Arrays

​1. Assigning by Index

​2. Inline Initialization

​Accessing Array Elements

​Get All Elements

​Quoting Arrays: Preserve Whitespace

​Modifying Arrays

​Append an Element

​Overwrite Entire Array

​Further Reading and References

Watch Video

Why Use Arrays?

Declaring Arrays

1. Assigning by Index

2. Inline Initialization

Accessing Array Elements

Get All Elements

Quoting Arrays: Preserve Whitespace

Modifying Arrays

Append an Element

Overwrite Entire Array

Further Reading and References