Iterating over arrays in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print each element of the array.

Bash Scripting

arr=(apple banana cherry)
for item in [1]; do
  echo "$item"
done

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

A${arr[@]}

B$arr

C${arr}

D$arr[@]

Attempts:

3 left

💡 Hint

Common Mistakes

Using $arr instead of ${arr[@]} which only gives the first element.

Using ${arr} which does not expand all elements.

Using $arr[@] which is incorrect syntax.

Use ${arr[@]} to iterate over all elements of the array in bash.

2fill in blank

medium

Complete the code to get the length of the array.

Bash Scripting

arr=(dog cat mouse)
length=[1]
echo "Length is $length"

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

A${arr}

B${arr[@]}

C${#arr[@]}

D${#arr}

Attempts:

3 left

💡 Hint

Common Mistakes

Using ${#arr} which gives length of first element string, not array length.

Using ${arr[@]} which expands elements, not length.

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

3fill in blank

hard

Fix the error in the code to correctly iterate over the array elements.

Bash Scripting

fruits=(mango orange pineapple)
for fruit in [1]; do
  echo "$fruit"
done

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

A$fruits

B${fruits}

C$fruits[@]

D${fruits[@]}

Attempts:

3 left

💡 Hint

Common Mistakes

Using $fruits which only gives first element.

Using $fruits[@] which is invalid syntax.

Use ${fruits[@]} to correctly expand all elements for iteration.

4fill in blank

hard

Fill both blanks to create an array and print its elements using a loop.

Bash Scripting

my_array=([1])
for element in [2]; do
  echo "$element"
done

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

A"red" "green" "blue"

B${my_array}

C${my_array[@]}

Dmy_array

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting array elements causing word splitting.

Using ${my_array} which only expands first element.

Use quotes to define array elements and ${my_array[@]} to iterate all elements.

5fill in blank

hard

Fill all three blanks to create an array, get its length, and print each element.

Bash Scripting

colors=([1])
count=[2]
echo "Total colors: $count"
for color in [3]; do
  echo "$color"
done

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

A"yellow" "purple" "cyan"

B${#colors[@]}

C${colors[@]}

D${colors}

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted elements causing word splitting.

Using ${colors} instead of ${colors[@]} in the loop.

Using ${#colors} which gives length of first element string.

Define array with quoted elements, get length with ${#colors[@]}, iterate with ${colors[@]}.

Practice

1. What is the correct way to iterate over all elements in a Bash array named fruits?

easy

A. for fruit in ${fruits[*]}; do echo "$fruit"; done

B. for fruit in ${fruits}; do echo "$fruit"; done

C. for fruit in "${fruits[@]}"; do echo "$fruit"; done

D. for fruit in fruits; do echo "$fruit"; done

Solution

1. Step 1: Understand array iteration syntax

   In Bash, to iterate over all elements of an array safely, you use "${array[@]}" which expands each element as a separate word, preserving spaces.

2. Step 2: Check each option's correctness

   for fruit in "${fruits[@]}"; do echo "$fruit"; done uses "${fruits[@]}" correctly. Options B and C omit quotes or use ${fruits} or ${fruits[*]} without quotes, which can break elements with spaces. for fruit in fruits; do echo "$fruit"; done treats fruits as a string, not an array.

3. Final Answer:

   for fruit in "${fruits[@]}"; do echo "$fruit"; done -> Option C

4. Quick Check:

   Use "${array[@]}" to iterate safely [OK]

Hint: Always quote "${array[@]}" to handle spaces safely [OK]

Common Mistakes:

• Not quoting "${array[@]}" causing word splitting
• Using ${array} instead of ${array[@]}
• Iterating over the array name as a string

2. Which of the following is the correct syntax to iterate over an array colors in Bash?

easy

A. for color in colors; do echo $color; done

B. for color in ${colors}; do echo $color; done

C. for color in ${colors[@]}; do echo $color; done

D. for color in "${colors[@]}"; do echo $color; done

Solution

1. Step 1: Identify correct quoting for array iteration

   To iterate over array elements safely, you must quote "${array[@]}" to preserve elements with spaces.

2. Step 2: Evaluate each option

   for color in "${colors[@]}"; do echo $color; done correctly uses quotes around "${colors[@]}". for color in colors; do echo $color; done treats 'colors' as a string, not an array. for color in ${colors[@]}; do echo $color; done misses quotes, risking word splitting. for color in ${colors}; do echo $color; done uses ${colors} which is incorrect for arrays.

3. Final Answer:

   for color in "${colors[@]}"; do echo $color; done -> Option D

4. Quick Check:

   Quote "${array[@]}" for safe iteration [OK]

Hint: Quote "${array[@]}" to avoid splitting elements [OK]

Common Mistakes:

• Forgetting quotes around "${array[@]}"
• Using array name without $ or quotes
• Using ${array} instead of ${array[@]}

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

names=("Alice" "Bob Smith" "Charlie")
for name in "${names[@]}"; do
  echo "$name"
done

medium

A. Alice
Bob Smith
Charlie

B. Alice
Bob
Smith
Charlie

C. Alice Bob Smith Charlie

D. Syntax error

Solution

1. Step 1: Understand array elements and quoting

   The array has three elements: "Alice", "Bob Smith", and "Charlie". Quoting "${names[@]}" preserves each element as one word, even if it contains spaces.

2. Step 2: Trace the loop output

   The loop prints each element on its own line: first "Alice", then "Bob Smith", then "Charlie".

3. Final Answer:

   Alice Bob Smith Charlie -> Option A

4. Quick Check:

   Quoted "${array[@]}" keeps elements intact [OK]

Hint: Quoted "${array[@]}" keeps multi-word elements together [OK]

Common Mistakes:

• Assuming elements split on spaces inside quotes
• Using unquoted ${array[@]} causing word splitting
• Expecting all elements on one line

4. Identify the error in this Bash script that tries to print all elements of array items:

items=("pen" "notebook" "eraser")
for i in ${items[@]}
do
  echo $i
done

medium

A. Array declaration syntax is wrong

B. Missing quotes around ${items[@]} causes word splitting

C. for loop syntax is incorrect

D. echo command is missing quotes

Solution

1. Step 1: Check array declaration

   The array declaration is correct with parentheses and quoted elements.

2. Step 2: Analyze the for loop iteration

   The loop uses unquoted ${items[@]}, which causes word splitting. If any element had spaces, it would split incorrectly. Quoting "${items[@]}" fixes this.

3. Final Answer:

   Missing quotes around ${items[@]} causes word splitting -> Option B

4. Quick Check:

   Always quote "${array[@]}" to avoid splitting [OK]

Hint: Quote "${array[@]}" to prevent splitting elements [OK]

Common Mistakes:

• Not quoting array expansion in loops
• Assuming echo needs quotes for correctness here
• Misreading array declaration syntax

5. You have a Bash array files containing filenames, some with spaces. You want to print only those filenames that contain the word "report". Which script correctly iterates and filters the array?

hard

A. for file in "${files[@]}"; do if [[ $file == *report* ]]; then echo "$file"; fi; done

B. for file in ${files[@]}; do if [[ $file == *report* ]]; then echo "$file"; fi; done

C. for file in "${files[*]}"; do if [[ $file == *report* ]]; then echo "$file"; fi; done

D. for file in files; do if [[ $file == *report* ]]; then echo "$file"; fi; done

Solution

1. Step 1: Choose correct array iteration with quoting

   To handle filenames with spaces correctly, iterate using "${files[@]}" quoted. This preserves each filename as one item.

2. Step 2: Apply filtering condition inside loop

   The condition [[ $file == *report* ]] correctly checks if the filename contains "report". for file in "${files[@]}"; do if [[ $file == *report* ]]; then echo "$file"; fi; done uses this with proper quoting and iteration.

3. Final Answer:

   for file in "${files[@]}"; do if [[ $file == *report* ]]; then echo "$file"; fi; done -> Option A

4. Quick Check:

   Quote "${array[@]}" and filter inside loop [OK]

Hint: Quote "${array[@]}" and filter inside loop with [[ ]] [OK]

Common Mistakes:

• Using unquoted ${files[@]} splitting filenames
• Using ${files[*]} which joins all elements into one string
• Iterating over literal 'files' string