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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.

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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 TypeIndexing MethodDeclaration
Indexed ArrayNumeric, 0-baseddeclare -a arr=(...)
Associative ArrayString-based keysdeclare -A arr=(...)

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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

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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.

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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

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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

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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.

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Example: Email Addresses

#!/usr/bin/env bash
declare -A email_addresses=(
  ["Mark"]="[email protected]"
  ["Kriti"]="[email protected]"
  ["Feng"]="[email protected]"
)

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

$ ./email-1.sh
[email protected]

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Adding New Elements

Assign a key in square brackets to insert or append: 
#!/usr/bin/env bash
declare -A email_addresses=(
  ["Mark"]="[email protected]"
  ["Kriti"]="[email protected]"
  ["Feng"]="[email protected]"
)

# Add more contacts
email_addresses["Andy"]="[email protected]"
email_addresses["Rajasekar"]="[email protected]"

echo "${email_addresses[@]}"

$ ./email-3.sh
[email protected] [email protected] ...
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.

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Replacing a Value

Overwrite an existing key to update its value: 
#!/usr/bin/env bash
declare -A email_addresses=(
  ["Mark"]="[email protected]"
  ["Kriti"]="[email protected]"
  ["Feng"]="[email protected]"
  ["Rajasekar"]="[email protected]"
)

echo "Before: ${email_addresses[@]}"
email_addresses["Feng"]="[email protected]"
echo "After:  ${email_addresses[@]}"

$ ./email-4.sh
Before: [email protected] ...
After:  [email protected] ... [email protected]

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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

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Listing Keys vs. Values

  • Keys: ${!array[@]}
  • Values: ${array[@]}
#!/usr/bin/env bash
declare -A email_addresses=( ... )

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

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

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