Array slicing in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Bash array slicing?

Given the array arr=(a b c d e f g), what is the output of echo ${arr[@]:2:3}?

Bash Scripting

arr=(a b c d e f g)
echo ${arr[@]:2:3}

A d e f

B b c d

C a b c

D c d e

💡 Hint

Remember that array slicing starts at index 0 and the syntax is ${array[@]:start:length}.

The slice starts at index 2 (third element) and takes 3 elements: c, d, e.

💻 Command Output

intermediate

What does this negative index slice output?

With arr=(1 2 3 4 5 6 7 8 9), what is the output of echo ${arr[@]: -4:2}?

Bash Scripting

arr=(1 2 3 4 5 6 7 8 9)
echo ${arr[@]: -4:2}

A 8 9

B 6 7

C 7 8

D 5 6

💡 Hint

Negative start index counts from the end of the array.

Start index -4 means start at the 4th last element, which is 6, then take 2 elements: 6 and 7.

📝 Syntax

advanced

Which option correctly slices the last 3 elements of an array?

Given arr=(x y z a b c d), which command outputs the last 3 elements?

Bash Scripting

arr=(x y z a b c d)

A echo ${arr[@]: -3:3}

B echo ${arr[@]:3:3}

C echo ${arr[@]: -3}

D echo ${arr[@]: -4:3}

💡 Hint

Use negative start index and specify length to get exact elements.

Option A starts 3 from the end and takes 3 elements, correctly outputting 'b c d'. Option A omits length and outputs 3 elements but may be ambiguous. Option A starts at index 3, which is 'a', not last 3. Option A starts 4 from end and takes 3 elements, which is 'a b c'.

🔧 Debug

advanced

Why does this slicing command fail?

Given arr=(10 20 30 40 50), why does echo ${arr[@]:-3:2} produce unexpected output?

Bash Scripting

arr=(10 20 30 40 50)
echo ${arr[@]:-3:2}

A Because the syntax ${arr[@]:-3:2} is interpreted as a default value, not slicing

B Because negative indices must have a space after the colon to be recognized

C Because there is no space after the colon before the negative index

D Because the array is too short for this slice

💡 Hint

Check how Bash interprets the colon and minus sign in parameter expansion.

Without a space, ${arr[@]:-3:2} is interpreted as 'if arr[@] is unset or null, use -3:2', not slicing. To slice with negative index, a space is needed after the colon: ${arr[@]: -3:2}.

🚀 Application

expert

How many elements are in the slice?

Given arr=(alpha beta gamma delta epsilon zeta eta), what is the number of elements output by echo ${arr[@]:4:10}?

Bash Scripting

arr=(alpha beta gamma delta epsilon zeta eta)
echo ${arr[@]:4:10}

A 4

B 7

C 3

D 10

💡 Hint

The slice length can be longer than the remaining elements, but output only includes available elements.

Starting at index 4 (epsilon), there are only 3 elements left: epsilon, zeta, eta. The length 10 is more than available, so only 3 elements are output.

Practice

1. In Bash scripting, what does array slicing do when you use ${array[@]:start:length}?

easy

A. Sorts the array elements alphabetically

B. Deletes elements from the array starting at start index

C. Extracts a part of the array starting at start index with length elements

D. Reverses the array elements from start to length

Solution

1. Step 1: Understand array slicing syntax

   In Bash, ${array[@]:start:length} extracts elements from the array starting at index start and takes length elements.

2. Step 2: Compare options with this behavior

   Only Extracts a part of the array starting at start index with length elements correctly describes this extraction. Other options describe unrelated operations.

3. Final Answer:

   Extracts a part of the array starting at start index with length elements -> Option C

4. Quick Check:

   Array slicing = Extract part [OK]

Hint: Remember slicing picks elements, not deletes or sorts [OK]

Common Mistakes:

• Confusing slicing with deleting elements
• Thinking slicing sorts or reverses the array
• Mixing up start index and length meaning

2. Which of the following is the correct syntax to slice 3 elements from index 2 in a Bash array named arr?

easy

A. ${arr[2:3]}

B. ${arr[@]:2:3}

C. ${arr:2:3}

D. ${arr[2..4]}

Solution

1. Step 1: Recall correct array slicing syntax

   In Bash, to slice an array, use ${array[@]:start:length}. The @ is needed to refer to all elements.

2. Step 2: Check each option

   ${arr[@]:2:3} matches the correct syntax: ${arr[@]:2:3}. ${arr:2:3} misses @, which is required for arrays. Options B and D use invalid syntax.

3. Final Answer:

   ${arr[@]:2:3} -> Option B

4. Quick Check:

   Use ${array[@]:start:length} for slicing [OK]

Hint: Use @ inside braces for array slicing syntax [OK]

Common Mistakes:

• Omitting @ when slicing arrays
• Using square brackets with colon syntax
• Trying to slice with invalid range notation

3. Given the Bash array arr=(a b c d e), what is the output of echo ${arr[@]:1:3}?

medium

A. a b c

B. c d e

C. b c d e

D. b c d

Solution

1. Step 1: Identify the array and slice parameters

   The array is (a b c d e). The slice starts at index 1 and takes 3 elements.

2. Step 2: Extract elements from index 1 to 3

   Index 0 = a, 1 = b, 2 = c, 3 = d, 4 = e. Taking 3 elements from index 1 gives: b, c, d.

3. Final Answer:

   b c d -> Option D

4. Quick Check:

   Slice from 1 length 3 = b c d [OK]

Hint: Count from zero, pick length elements starting at start [OK]

Common Mistakes:

• Starting count at 1 instead of 0
• Taking wrong number of elements
• Confusing output with full array

4. What is wrong with this Bash code snippet for slicing an array?

arr=(x y z)
echo ${arr:1:2}

medium

A. It will output an empty string

B. It will output only one element instead of two

C. It will cause a syntax error because slicing is not allowed

D. It will output 'y z' correctly

Solution

1. Step 1: Check slicing syntax correctness

   The code uses ${arr:1:2} without @. For arrays, @ is needed to slice multiple elements.

2. Step 2: Understand the effect of missing @

   Without @, Bash uses the first element x as a scalar string and slices it from index 1 length 2. Since x has length 1, it outputs an empty string.

3. Final Answer:

   It will output an empty string -> Option A

4. Quick Check:

   Missing @ slices first elem as string -> empty [OK]

Hint: Always use @ for array slicing, else string slicing happens [OK]

Common Mistakes:

• Omitting @ and expecting array slice
• Assuming no error but wrong output
• Confusing string and array slicing syntax

5. You have a Bash array arr=(1 2 3 4 5). You want to extract the last 3 elements using array slicing. Which command will do this correctly?

hard

A. echo ${arr[@]:-3}

B. echo ${arr[@]: -3:3}

C. echo ${arr[@]:3:3}

D. echo ${arr[@]:3}

Solution

1. Step 1: Understand negative index slicing in Bash

   Using a negative start index slices from the end. ${arr[@]:-3} extracts from 3rd from end to the end (last 3 elements).

2. Step 2: Check each option

   ${arr[@]: -3:3} has space after : causing bad substitution. ${arr[@]:3:3} slices from index 3 length 3 but only 2 elements remain (4 5). ${arr[@]:3} slices from 3 to end (4 5). Only ${arr[@]:-3} gets exactly the last 3: 3 4 5.

3. Final Answer:

   echo ${arr[@]:-3} -> Option A

4. Quick Check:

   Negative start index slices from end [OK]

Hint: Use negative start index without length to get last elements [OK]

Common Mistakes:

• Adding space after ':' before negative offset
• Using slice length larger than remaining elements
• Not knowing negative indices slice from array end