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]}"
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
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".
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.
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.
Links and References 
