Array length in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Bash script?

Consider the following Bash script that defines an array and prints its length. What will be the output?

Bash Scripting

arr=(apple banana cherry date)
echo ${#arr[@]}

A 4

B 1

C 3

D Syntax error

💡 Hint

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

The array 'arr' has 4 elements: apple, banana, cherry, and date. Using ${#arr[@]} returns the count of elements, which is 4.

💻 Command Output

intermediate

What does this script print?

Given this Bash script, what is the output?

Bash Scripting

arr=(one two three)
echo ${#arr}

A 11

B 3

C Syntax error

D 0

💡 Hint

${#arr} returns the length of the first element, not the number of elements.

${#arr} without [@] or [0] returns the length of the first element of the array, which is 'one' with 3 characters.

💻 Command Output

advanced

What is the output of this Bash script with sparse array?

Consider this Bash script where an array has elements assigned at non-contiguous indices. What will be the output?

Bash Scripting

arr=()
arr[0]=zero
arr[3]=three
arr[5]=five
echo ${#arr[@]}

A Syntax error

B 5

C 3

D 6

💡 Hint

Array length counts the number of elements, not the highest index.

The array has elements at indices 0, 3, and 5, so total 3 elements. ${#arr[@]} returns 3.

💻 Command Output

advanced

What does this script output when printing array length?

What is the output of this Bash script?

Bash Scripting

arr=(a b c d e)
length=${#arr[@]}
echo $length
unset arr[2]
echo ${#arr[@]}

A Syntax error

B

5
5

C

5
3

D

5
4

💡 Hint

Unsetting an element removes it, reducing the count.

Initially, the array has 5 elements. After unsetting index 2, the element is removed, so length becomes 4.

💻 Command Output

expert

What is the output of this Bash script with indirect reference?

Given this script, what will be the output?

Bash Scripting

arr=(x y z)
name=arr
echo ${#name[@]}
echo ${#arr[@]}

A

1
3

B

3
3

C

Syntax error
3

D

0
3

💡 Hint

Variable name is a string, not an array reference.

${#name[@]} returns 1 because 'name' is a string variable, not an array. ${#arr[@]} returns 3.

Practice

1. In bash scripting, which expression correctly gives the number of elements in an array named my_array?

easy

A. ${#my_array[@]}

B. ${my_array[@]}

C. ${#my_array}

D. ${my_array}

Solution

1. Step 1: Understand array length syntax

   In bash, ${#array[@]} returns the count of elements in the array.

2. Step 2: Differentiate from other forms

   ${#array} returns the length of the first element, not the number of elements.

3. Final Answer:

   ${#my_array[@]} -> Option A

4. Quick Check:

   Array length = ${#my_array[@]} [OK]

Hint: Use ${#array[@]} to get array size, not ${#array} [OK]

Common Mistakes:

• Using ${#array} which gives length of first element
• Using ${array[@]} which expands elements, not count
• Confusing ${array} with array length

2. Which of the following is the correct syntax to store the length of a bash array files into a variable count?

easy

A. count=${files[@]}

B. count=${#files}

C. count=${#files[@]}

D. count=${files}

Solution

1. Step 1: Use correct length syntax

   To get the number of elements, use ${#files[@]}.

2. Step 2: Assign to variable

   Assigning with count=${#files[@]} stores the array length in count.

3. Final Answer:

   count=${#files[@]} -> Option C

4. Quick Check:

   Variable count = ${#files[@]} [OK]

Hint: Assign length with count=${#array[@]} to get element count [OK]

Common Mistakes:

• Using count=${files[@]} which assigns all elements, not length
• Using count=${#files} which gives length of first element
• Forgetting to use ${} around the expression

3. What will be the output of this bash script?

arr=(apple banana cherry)
echo ${#arr[@]}

medium

A. apple

B. 18

C. 0

D. 3

Solution

1. Step 1: Understand array initialization

   The array arr has 3 elements: apple, banana, cherry.

2. Step 2: Use ${#arr[@]} to get count

   ${#arr[@]} returns the number of elements, which is 3.

3. Final Answer:

   3 -> Option D

4. Quick Check:

   Array length = 3 [OK]

Hint: Count elements with ${#array[@]} to get number, not string length [OK]

Common Mistakes:

• Confusing ${#arr[@]} with ${#arr} which gives length of first element
• Expecting total string length instead of element count
• Printing array without expansion

4. Identify the error in this bash script snippet that tries to print the number of elements in array data:

data=(1 2 3 4)
echo ${#data}

medium

A. It prints the length of the first element, not the array size

B. The array is not declared properly

C. The echo command is missing quotes

D. The syntax ${#data} is invalid in bash

Solution

1. Step 1: Check array length syntax

   ${#data} returns the length of the first element (string length), not the number of elements.

2. Step 2: Correct syntax for array length

   Use ${#data[@]} to get the count of elements in the array.

3. Final Answer:

   It prints the length of the first element, not the array size -> Option A

4. Quick Check:

   Use ${#array[@]} for count, not ${#array} [OK]

Hint: Use ${#array[@]} to get count, ${#array} gives first element length [OK]

Common Mistakes:

• Assuming ${#array} gives number of elements
• Not using [@] inside the braces
• Thinking echo needs quotes for this syntax

5. You have a bash array items that may be empty or have elements. You want to print "Empty" if it has zero elements, or "Count: N" where N is the number of elements. Which script snippet correctly does this?

hard

A. if [ ${#items} -eq 0 ]; then echo "Empty"; else echo "Count: ${#items[@]}"; fi

B. if [ ${#items[@]} -eq 0 ]; then echo "Empty"; else echo "Count: ${#items[@]}"; fi

C. if [ ${#items[@]} -eq 0 ]; then echo "Empty"; else echo "Count: ${#items}"; fi

D. if [ ${#items} -eq 0 ]; then echo "Empty"; else echo "Count: ${#items}"; fi

Solution

1. Step 1: Check condition for empty array

   Use ${#items[@]} to get the number of elements. If zero, array is empty.

2. Step 2: Print count correctly

   Use ${#items[@]} to print the count of elements, not ${#items} which is length of first element.

3. Final Answer:

   if [ ${#items[@]} -eq 0 ]; then echo "Empty"; else echo "Count: ${#items[@]}"; fi -> Option B

4. Quick Check:

   Use ${#array[@]} for count in both condition and output [OK]

Hint: Always use ${#array[@]} to check and print array length [OK]

Common Mistakes:

• Using ${#array} instead of ${#array[@]} for count
• Mixing length of first element with element count
• Forgetting to use [ ] in if condition