Master Bash Associative Arrays: Declaration, Access, Traversal, and Real-World Uses

Introduction

In Bash scripting, arrays are common, but traditional indexed arrays lack flexibility. Bash 4.0 and later introduce associative arrays, allowing string keys similar to maps or dictionaries in other languages. This article details their usage and practical applications.

Declaring and Initializing an Associative Array

Use the declare -A keyword to create an associative array. The example below declares myMap and adds three key‑value pairs.

#!/bin/bash
# Declare an associative array
declare -A myMap

# Add key‑value pairs
myMap["name"]="Alice"
myMap["age"]="28"
myMap["city"]="Seattle"

The script creates myMap with keys name, age, and city, each storing a string value.

Accessing Elements

Elements are accessed using their string keys, just like indexed arrays but with the key name.

#!/bin/bash
declare -A myMap
myMap["name"]="Alice"
myMap["age"]="28"
myMap["city"]="Seattle"

echo "Name: ${myMap["name"]}"
echo "Age: ${myMap["age"]}"
echo "City: ${myMap["city"]}"

Running the script outputs:

Name: Alice
Age: 28
City: Seattle

Iterating Over an Associative Array

The for loop can iterate over all keys using ${!myMap[@]}, then retrieve each value.

#!/bin/bash
declare -A myMap
myMap["name"]="Alice"
myMap["age"]="28"
myMap["city"]="Seattle"

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

Output:

name: Alice
age: 28
city: Seattle

Removing Elements

The unset command deletes a specific key from the array.

#!/bin/bash
declare -A myMap
myMap["name"]="Alice"
myMap["age"]="28"
myMap["city"]="Seattle"

unset myMap["age"]

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

Output after removal:

name: Alice
city: Seattle

Checking for a Key

Use an if statement with the -v test to verify a key’s existence.

#!/bin/bash
declare -A myMap
myMap["name"]="Alice"
myMap["age"]="28"
myMap["city"]="Seattle"

if [[ -v myMap["age"] ]]; then
    echo "Age exists in the array."
else
    echo "Age does not exist in the array."
fi

Running the script prints:

Age exists in the array.

Practical Use: Word‑Frequency Counter

Associative arrays are handy for counting occurrences, such as word frequencies in a string.

#!/bin/bash
declare -A wordCount

text="this is a test this is only a test"

for word in $text; do
    ((wordCount[$word]++))
 done

for word in "${!wordCount[@]}"; do
    echo "$word: ${wordCount[$word]}"
 done

Output:

this: 2
is: 2
a: 2
test: 2
only: 1

Conclusion

Associative arrays greatly enhance Bash scripting by providing flexible key‑value storage, enabling more readable and efficient scripts for configuration handling, JSON parsing, word‑frequency analysis, and other tasks. Mastering declaration, access, iteration, deletion, and key checks empowers developers to write better shell code.