Array slicing in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to extract the first three elements from the array.

Bash Scripting

arr=(apple banana cherry date)
slice=(${arr[@]:[1]:3})
echo "${slice[@]}"

Drag options to blanks, or click blank then click option'

A2

B1

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Starting the slice at 1 will skip the first element.

Using a length other than 3 will give wrong number of elements.

In bash, array slicing starts at index 0. To get the first three elements, start at 0 and take 3 elements.

2fill in blank

medium

Complete the code to extract elements starting from the second element to the end.

Bash Scripting

arr=(red green blue yellow)
slice=(${arr[@]:[1])
echo "${slice[@]}"

Drag options to blanks, or click blank then click option'

A0

B1

C3

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 0 extracts the whole array.

Starting at 2 skips the second element.

Starting at index 1 extracts elements from the second element to the end.

3fill in blank

hard

Fix the error in the code to correctly slice the array from the third element, taking two elements.

Bash Scripting

arr=(one two three four five)
slice=(${arr[@]:[1]:2})
echo "${slice[@]}"

Drag options to blanks, or click blank then click option'

A2

B1

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 starts from the fourth element, not third.

Using index 1 starts from the second element.

Index 2 corresponds to the third element in the array, so slicing from 2 with length 2 extracts the third and fourth elements.

4fill in blank

hard

Fill both blanks to slice the array from the second element and take three elements.

Bash Scripting

arr=(cat dog bird fish horse)
slice=(${arr[@]:[1]:[2])
echo "${slice[@]}"

Drag options to blanks, or click blank then click option'

A1

B2

C3

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 2 skips the second element.

Taking 2 elements returns fewer than needed.

Start at index 1 (second element) and take 3 elements to get dog, bird, fish.

5fill in blank

hard

Complete the code to extract the last three elements from the array using a negative index.

Bash Scripting

arr=(apple bat cherry dog elephant fox)
slice=(${arr[@]:[1])
echo "${slice[@]}"

Drag options to blanks, or click blank then click option'

A3

B-1

C0

D-3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 extracts from index 3 to end, which happens to be the same here, but positive indexes count from the start.

Using 0 extracts the entire array.

Using -1 extracts only the last element.

Using a negative index -3 in the slice extracts the last three elements: dog elephant fox.

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