Associative

In this tutorial, you will explore associative arrays in Bash—powerful data structures that use named keys for direct value lookup. By the end, you’ll understand how to declare, access, modify, and iterate over associative arrays in your scripts.

Indexed Arrays vs. Associative Arrays

Think of indexed arrays as a numbered chest of drawers (0-based), and associative arrays as labeled drawers you open by name.

Array Type	Indexing Method	Declaration
Indexed Array	Numeric, 0-based	`declare -a arr=(...)`
Associative Array	String-based keys	`declare -A arr=(...)`

Example: Indexed Array (Socks Analogy)

#!/usr/bin/env bash
declare -a chest_drawer=("shirts" "sports clothing" "socks" "jeans")
echo "${chest_drawer[2]}"

$ ./socks.sh
socks

Checking Your Bash Version

Associative arrays require Bash 4.0+. Verify with:

$ echo $BASH_VERSION
5.2.15(1)-release

If your Bash version is older than 4.0, associative arrays won’t work. Please upgrade before continuing.

Declaring and Accessing an Associative Array

Use declare -A to define an associative array. Here’s how to store and retrieve “socks” by key:

#!/usr/bin/env bash
declare -A chest_drawer=(
  ["shirts"]="T-Shirts and polo shirts"
  ["sports"]="All sorts of Sports Clothing here"
  ["socks"]="Formal and everyday socks"
  ["jeans"]="Jeans, and some casual dress shorts"
)

echo "${chest_drawer["socks"]}"

$ ./associative-v1.sh
Formal and everyday socks

Analogy: Emergency Contacts

Store quick-dial numbers by department name:

#!/usr/bin/env bash
declare -A emergency_contacts=(
  ["Fire Department"]="555-0001"
  ["Police Department"]="555-0002"
  ["Hospital"]="555-0003"
)

echo "${emergency_contacts["Fire Department"]}"

$ ./emergency.sh
555-0001

Key-Value Pair Concept

Associative arrays map keys (identifiers) to values (data).

In Bash associative arrays, each key is unique and case-sensitive: "Mark" ≠ "mark".

The image explains associative arrays, highlighting the concepts of "key" as an identifier and "value" as the actual data to interact with.

Example: Email Addresses

#!/usr/bin/env bash
declare -A email_addresses=(
  ["Mark"]="mark@email.com"
  ["Kriti"]="kriti@email.com"
  ["Feng"]="feng@email.com"
)

echo "${email_addresses["Mark"]}"

$ ./email-1.sh
mark@email.com

Adding New Elements

Assign a key in square brackets to insert or append:

#!/usr/bin/env bash
declare -A email_addresses=(
  ["Mark"]="mark@email.com"
  ["Kriti"]="kriti@email.com"
  ["Feng"]="feng@email.com"
)

# Add more contacts
email_addresses["Andy"]="andy@email.com"
email_addresses["Rajasekar"]="rajasekar@email.com"

echo "${email_addresses[@]}"

$ ./email-3.sh
mark@email.com rajasekar@email.com ...

Associative arrays are unordered; iteration order can vary.

The image is a slide about associative arrays, highlighting that they do not consider the order in which elements are stored.

Replacing a Value

Overwrite an existing key to update its value:

#!/usr/bin/env bash
declare -A email_addresses=(
  ["Mark"]="mark@email.com"
  ["Kriti"]="kriti@email.com"
  ["Feng"]="feng@email.com"
  ["Rajasekar"]="rajasekar@email.com"
)

echo "Before: ${email_addresses[@]}"
email_addresses["Feng"]="feng2@email.com"
echo "After:  ${email_addresses[@]}"

$ ./email-4.sh
Before: kriti@email.com ...
After:  kriti@email.com ... feng2@email.com

Removing Elements

Use unset to delete by key or clear the entire array:

#!/usr/bin/env bash
declare -A email_addresses=( ... )

# Remove one element
unset email_addresses["Kriti"]

# Remove all elements
unset email_addresses

Listing Keys vs. Values

Keys: ${!array[@]}
Values: ${array[@]}

#!/usr/bin/env bash
declare -A email_addresses=( ... )

echo "Keys:   ${!email_addresses[@]}"
echo "Values: ${email_addresses[@]}"

Iterating with a `for` Loop

Loop through keys and access each value:

#!/usr/bin/env bash
declare -A email_addresses=( ... )

for key in "${!email_addresses[@]}"; do
  echo "$key's email is ${email_addresses[$key]}"
done

$ ./email-8.sh
Kriti's email is kriti@email.com
...

Enclose "${!email_addresses[@]}" in quotes to handle multi-word keys correctly.

Introduction

Conventions

Refresher

Streams

Expansions - Part One

Globs

Expansions - Part Two

Special Shell Variables

Arrays

Good Practices applied

awk

sed

Indexed Arrays vs. Associative Arrays

Example: Indexed Array (Socks Analogy)

Checking Your Bash Version

Declaring and Accessing an Associative Array

Analogy: Emergency Contacts

Key-Value Pair Concept

Example: Email Addresses

Adding New Elements

Replacing a Value

Removing Elements

Listing Keys vs. Values

Iterating with a `for` Loop

Links and References

Watch Video

​Indexed Arrays vs. Associative Arrays

​Example: Indexed Array (Socks Analogy)

​Checking Your Bash Version

​Declaring and Accessing an Associative Array

​Analogy: Emergency Contacts

​Key-Value Pair Concept

​Example: Email Addresses

​Adding New Elements

​Replacing a Value

​Removing Elements

​Listing Keys vs. Values

​Iterating with a for Loop

​Links and References

Watch Video

Indexed Arrays vs. Associative Arrays

Example: Indexed Array (Socks Analogy)

Checking Your Bash Version

Declaring and Accessing an Associative Array

Analogy: Emergency Contacts

Key-Value Pair Concept

Example: Email Addresses

Adding New Elements

Replacing a Value

Removing Elements

Listing Keys vs. Values

Iterating with a `for` Loop

Links and References