How to Use Associative Arrays in Bash: Syntax and Examples

In Bash, you create an associative array using declare -A array_name. You can then assign values with keys like array_name[key]=value and access them using ${array_name[key]}.

Syntax

To use an associative array in Bash, first declare it with declare -A. Then assign values using keys inside square brackets. Access values with ${array_name[key]}.

• declare -A array_name: Creates an associative array.
• array_name[key]=value: Assigns a value to a key.
• ${array_name[key]}: Retrieves the value for a key.

bash

declare -A my_array
my_array[key1]=value1
my_array[key2]=value2

# Access value
echo "${my_array[key1]}"

Output

value1

Example

This example shows how to declare an associative array, add key-value pairs, and print all keys and values.

bash

declare -A colors
colors[apple]=red
colors[banana]=yellow
colors[grape]=purple

# Print a single value
echo "Color of apple: ${colors[apple]}"

# Loop through all keys and print key-value pairs
for fruit in "${!colors[@]}"; do
  echo "$fruit is ${colors[$fruit]}"
done

Output

Color of apple: red
apple is red
banana is yellow
grape is purple

Common Pitfalls

Common mistakes include forgetting to declare the array with declare -A, which makes Bash treat it as a normal indexed array. Also, keys must be quoted if they contain spaces or special characters.

Wrong: my_array[key with space]=value (no quotes)

Right: my_array["key with space"]=value

bash

declare -A my_array

# Wrong: no quotes around key with space
# my_array[key with space]=value  # This causes an error

# Right: quotes around key
my_array["key with space"]=value

echo "${my_array[\"key with space\"]}"

Output

value

Quick Reference

Command	Description
declare -A array_name	Declare an associative array
array_name[key]=value	Assign value to a key
${array_name[key]}	Access value by key
${!array_name[@]}	Get all keys
${array_name[@]}	Get all values

Key Takeaways

Always declare associative arrays with declare -A before use.

Use quotes around keys if they contain spaces or special characters.

Access values with ${array_name[key]} and list keys with ${!array_name[@]}.

Associative arrays require Bash version 4.0 or higher.

Loop through keys to process all elements in the array.