🐚 Bash Arrays & Associative Arrays – arr=(), declare -A with Examples

Introduction to Bash Arrays – Indexed and Associative Arrays Explained

In Bash scripting, arrays let you store multiple values in a single variable, making your scripts more efficient and organized. Bash supports two types of arrays:

• Indexed arrays – accessed by numeric indexes
• Associative arrays – accessed using string keys

While indexed arrays are available by default, associative arrays require explicit declaration using declare -A.

In this article, you’ll learn:

• How to declare, access, and modify indexed arrays
• How to use associative arrays with string keys
• Syntax differences between the two array types
• Real-world examples and best practices

What Are Arrays in Bash?

Arrays in Bash allow you to group related data together. Instead of using separate variables like val1, val2, val3, you can group them as:

arr=(val1 val2 val3)

Indexed Arrays – Syntax and Usage

Declare an Indexed Array

fruits=("apple" "banana" "cherry")

Access Elements

echo ${fruits[0]}  # Output: apple
echo ${fruits[1]}  # Output: banana

Add or Update Elements

fruits[3]="orange"
fruits[1]="mango"

Loop Through Array

for fruit in "${fruits[@]}"; do
  echo "$fruit"
done

Get Array Length

echo ${#fruits[@]}  # Number of elements

Associative Arrays – Key-Value Storage

Declare an Associative Array

declare -A capitals

Add Elements

capitals[India]="New Delhi"
capitals[France]="Paris"
capitals[Japan]="Tokyo"

Access Elements

echo ${capitals[India]}  # Output: New Delhi

Loop Through Keys

for country in "${!capitals[@]}"; do
  echo "$country: ${capitals[$country]}"
done

Get All Keys or Values

echo "${!capitals[@]}"  # Keys
echo "${capitals[@]}"   # Values

Associative arrays require Bash version 4.0+ and must be declared using declare -A.

Example: Student Grades (Associative Array)

declare -A grades
grades[Alice]=95
grades[Bob]=88
grades[Charlie]=78

for student in "${!grades[@]}"; do
  echo "$student scored ${grades[$student]}"
done

Output:

Alice scored 95
Bob scored 88
Charlie scored 78

Common Mistakes to Avoid

Summary – Bash Arrays & Associative Arrays

Arrays bring structure and efficiency to Bash scripts. Use indexed arrays for ordered lists, and associative arrays when you need key-value mappings. Mastering both allows you to build advanced CLI tools and automate complex logic.

Key Takeaways:

• Use arr=(...) for indexed arrays
• Use declare -A arr for associative arrays
• Use "${arr[@]}" for safe iteration
• Associative arrays require Bash 4+

Real-world Uses:

• Manage user-role pairs
• Store filename-extension mappings
• Track counts, totals, or states in scripts

FAQ – Bash Arrays & Associative Arrays

How do I check the length of a Bash array?
Use:

echo ${#array[@]}

This returns the number of elements.

Can Bash arrays be multi-dimensional?
No native support, but you can simulate with naming conventions or indexed keys:

matrix[0,0]=1

Are associative arrays supported in all Bash versions?
No. Associative arrays are supported only in Bash 4.0 or newer.

How do I loop through both keys and values in associative arrays?
Use:

for key in "${!arr[@]}"; do
  echo "$key: ${arr[$key]}"
done

What’s the safest way to loop through an array with spaces?
Always quote:

for val in "${array[@]}"; do echo "$val"; done