Associative arrays (declare -A) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Associative Array Access

What is the output of this Bash script?

Bash Scripting

declare -A colors
colors[apple]=red
colors[banana]=yellow
colors[grape]=purple
echo ${colors[banana]}

A yellow

B red

C purple

D banana

💡 Hint

Look at the key used inside the brackets when accessing the array.

The script declares an associative array 'colors' and assigns colors to fruits. Accessing colors[banana] prints 'yellow'.

💻 Command Output

intermediate

Count Items in Associative Array

What is the output of this Bash script?

Bash Scripting

declare -A animals
animals[dog]=bark
animals[cat]=meow
animals[cow]=moo
animals[duck]=quack
echo ${#animals[@]}

A 4

B 3

C 0

D 1

💡 Hint

${#array[@]} gives the number of elements in the array.

The associative array 'animals' has 4 key-value pairs, so ${#animals[@]} outputs 4.

🔧 Debug

advanced

Identify the Error in Associative Array Declaration

What error does this Bash script produce?

Bash Scripting

colors=( [red]=apple [yellow]=banana )
echo ${colors[red]}

A bash: colors: unbound variable

B bash: colors: array assignment without declare -A

C bash: colors: command not found

D No error, outputs 'apple'

💡 Hint

Associative arrays require a special declaration in Bash.

Associative arrays must be declared with 'declare -A' before assigning key-value pairs. Without it, Bash treats it as a normal array and errors.

🚀 Application

advanced

Result of Looping Over Associative Array Keys

What will this Bash script output?

Bash Scripting

declare -A capitals
capitals[France]=Paris
capitals[Japan]=Tokyo
capitals[India]=NewDelhi
for country in "${!capitals[@]}"; do
  echo "$country: ${capitals[$country]}"
done

A Paris Tokyo NewDelhi

B

Paris: France
Tokyo: Japan
NewDelhi: India

C

France: Paris
Japan: Tokyo
India: NewDelhi

D France Japan India

💡 Hint

"${!array[@]}" gives all keys in the associative array.

The loop iterates over keys (countries) and prints each key with its value (capital). Output is each country and its capital separated by colon.

🧠 Conceptual

expert

Behavior of Unset Key in Associative Array

What is the output of this Bash script?

Bash Scripting

declare -A fruits
fruits[apple]=red
fruits[banana]=yellow
unset fruits[apple]
echo ${fruits[apple]:-none}

A yellow

B red

C banana

D none

💡 Hint

Unset removes the key, and the default value is used if key is missing.

The key 'apple' is removed with unset. Accessing fruits[apple] returns empty, so the default 'none' is printed.

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