Associative arrays (declare -A) in Bash Scripting - Mini Project: Build & Apply

Using Associative Arrays in Bash

📖 Scenario: You are managing a small store's inventory. You want to keep track of product prices using a simple script.

🎯 Goal: Create a Bash script that uses an associative array to store product names and their prices, then display the price of each product.

📋 What You'll Learn

Use an associative array declared with declare -A

Store exact product-price pairs as given

Use a for loop to iterate over the associative array

Print each product and its price in the format: Product: Price

💡 Why This Matters

🌍 Real World

Associative arrays help store and manage key-value pairs like product prices, user settings, or configuration options in scripts.

💼 Career

Knowing associative arrays is useful for automating tasks, managing data in scripts, and writing efficient shell scripts in system administration or DevOps roles.

1

Create an associative array with products and prices

Create an associative array called products using declare -A. Add these exact entries: apple=100, banana=40, orange=70.

Bash Scripting

# Create an associative array called products with the given entries
# Your code here

Hint

Use declare -A products to create the associative array. Then assign the key-value pairs inside parentheses.

2

Add a variable to count the number of products

Create a variable called count that stores the number of products in the products associative array.

Bash Scripting

declare -A products=( [apple]=100 [banana]=40 [orange]=70 )
# Create a variable count to hold the number of products
# Your code here

Hint

Use ${#products[@]} to get the number of keys in the associative array.

3

Loop through the associative array to print products and prices

Use a for loop with the variable product to iterate over the keys of products. Inside the loop, get the price using ${products[$product]}.

Bash Scripting

declare -A products=( [apple]=100 [banana]=40 [orange]=70 )
count=${#products[@]}
# Use a for loop to iterate over products and get each price
# Your code here

Hint

Use "${!products[@]}" to get all keys. Then access each value with ${products[$product]}.

4

Print each product and its price

Inside the for loop, print the product and price in the format: Product: Price. Use echo with the variables product and price.

Bash Scripting

declare -A products=( [apple]=100 [banana]=40 [orange]=70 )
count=${#products[@]}
for product in "${!products[@]}"; do
    price=${products[$product]}
    # Print product and price here
    # Your code here
done

Hint

Use echo "$product: $price" to print each pair.

Practice

1. What is the main purpose of using declare -A in a Bash script?

easy

A. To define a function

B. To declare a regular indexed array

C. To create an associative array with named keys

D. To start a loop

Solution

1. Step 1: Understand the role of declare -A

   This command is used in Bash to declare an associative array, which means the array uses named keys instead of numbers.

2. Step 2: Differentiate from other declarations

   Regular arrays use numbers as keys and are declared without -A. Functions and loops are declared differently.

3. Final Answer:

   To create an associative array with named keys -> Option C

4. Quick Check:

   declare -A means associative array [OK]

Hint: Remember: -A means associative array with named keys [OK]

Common Mistakes:

• Confusing associative arrays with regular indexed arrays
• Thinking declare -A creates a function
• Assuming declare -A starts a loop

2. Which of the following is the correct syntax to declare an associative array named colors in Bash?

easy

A. declare colors=(red green blue)

B. declare -A colors

C. array colors=(red green blue)

D. declare -a colors

Solution

1. Step 1: Identify the correct declaration for associative arrays

   In Bash, declare -A is used to declare associative arrays, so declare -A colors is correct.

2. Step 2: Understand other options

   declare -a is for indexed arrays, and the other options are invalid syntax for associative arrays.

3. Final Answer:

   declare -A colors -> Option B

4. Quick Check:

   Associative array declaration uses declare -A [OK]

Hint: Use declare -A to declare associative arrays [OK]

Common Mistakes:

• Using declare -a which is for indexed arrays
• Trying to assign values during declaration incorrectly
• Using invalid syntax like array keyword

3. What will be the output of the following Bash script?

declare -A fruits
fruits[apple]=red
fruits[banana]=yellow
for key in "${!fruits[@]}"; do
  echo "$key is ${fruits[$key]}"
done

medium

A. apple banana\nred yellow

B. red is apple\nyellow is banana

C. Syntax error

D. apple is red\nbanana is yellow

Solution

1. Step 1: Understand the associative array and loop

   The array fruits has keys 'apple' and 'banana' with values 'red' and 'yellow'. The loop iterates over keys and prints key and value pairs.

2. Step 2: Predict the output format

   Each line prints "key is value", so output lines are "apple is red" and "banana is yellow" (order may vary but both lines appear).

3. Final Answer:

   apple is red\nbanana is yellow -> Option D

4. Quick Check:

   Loop prints key and value pairs correctly [OK]

Hint: Loop keys with ${!array[@]} to access associative array keys [OK]

Common Mistakes:

• Printing values as keys or vice versa
• Expecting syntax error due to quotes
• Confusing indexed arrays with associative arrays

4. Identify the error in the following Bash script that uses an associative array:

declare -A animals
animals=([dog]=bark [cat]=meow)
echo ${animals[dog]}

medium

A. No error, script runs correctly

B. Associative array cannot be assigned values this way

C. Missing quotes around keys in assignment

D. Incorrect syntax for echo command

Solution

1. Step 1: Check associative array assignment syntax

   Assigning values with animals=([dog]=bark [cat]=meow) is valid syntax for associative arrays in Bash.

2. Step 2: Verify echo command usage

   echo ${animals[dog]} correctly prints the value for key 'dog'. No syntax errors present.

3. Final Answer:

   No error, script runs correctly -> Option A

4. Quick Check:

   Associative array assignment and access are correct [OK]

Hint: Assign associative arrays with ([key]=value ...) syntax [OK]

Common Mistakes:

• Thinking quotes are mandatory around keys in assignment
• Assuming echo syntax is wrong without quotes
• Confusing indexed array assignment with associative arrays

5. You want to create an associative array user_ages that stores names as keys and ages as values. Which script correctly adds entries and prints all names with their ages?

hard

A. declare -A user_ages
user_ages=( [Alice]=30 [Bob]=25 )
for name in "${!user_ages[@]}"; do
echo "$name is ${user_ages[$name]} years old"
done

B. declare user_ages
user_ages=( Alice=30 Bob=25 )
for name in "${user_ages[@]}"; do
echo "$name is ${user_ages[$name]} years old"
done

C. declare -A user_ages
user_ages=( Alice:30 Bob:25 )
for name in "${!user_ages[@]}"; do
echo "$name is ${user_ages[$name]} years old"
done

D. declare -a user_ages
user_ages=( [Alice]=30 [Bob]=25 )
for name in "${!user_ages[@]}"; do
echo "$name is ${user_ages[$name]} years old"
done

Solution

1. Step 1: Check declaration and assignment

   declare -A user_ages user_ages=( [Alice]=30 [Bob]=25 ) for name in "${!user_ages[@]}"; do echo "$name is ${user_ages[$name]} years old" done correctly declares an associative array with declare -A and assigns keys and values using ( [key]=value ) syntax.

2. Step 2: Verify loop and output

   The loop uses ${!user_ages[@]} to get keys and prints each name with its age correctly.

3. Final Answer:

   Option A script correctly adds and prints associative array entries -> Option A

4. Quick Check:

   Use declare -A and [key]=value syntax for associative arrays [OK]

Hint: Use declare -A and [key]=value syntax for associative arrays [OK]

Common Mistakes:

• Using declare -a which is for indexed arrays
• Incorrect key-value syntax like colons or missing brackets
• Looping over values instead of keys