Iterating over arrays in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of iterating over a bash array with spaces

What is the output of this bash script?

Bash Scripting

arr=("apple" "banana split" "cherry")
for item in "${arr[@]}"; do
  echo "$item"
done

A

apple
banana split
cherry

B

apple
banana
split
cherry

C apple banana split cherry

D

apple
banana split cherry

💡 Hint

Think about how double quotes affect array expansion in bash loops.

Using "${arr[@]}" with quotes preserves each array element as a single item, so 'banana split' stays together and prints on one line.

💻 Command Output

intermediate

Iterating over array indices in bash

What does this script output?

Bash Scripting

arr=(10 20 30)
for i in "${!arr[@]}"; do
  echo "$i:${arr[i]}"
done

A Syntax error

B

10:10
20:20
30:30

C

0:10
1:20
2:

D

0:10
1:20
2:30

💡 Hint

${!arr[@]} gives the indices of the array.

The loop iterates over indices 0,1,2 and prints index:value pairs.

📝 Syntax

advanced

Identify the syntax error in array iteration

Which option contains a syntax error when iterating over a bash array?

Bash Scripting

arr=(a b c)

A for i in ${arr[*]}; do echo $i; done

B for i in "${arr[@]}"; do echo $i; done

C for i in ${arr[)}; do echo $i; done

D for i in ${arr[@]}; do echo $i; done

💡 Hint

Check how arrays are expanded in bash.

Option C has an invalid array index ${arr[)} which causes a 'bad substitution' syntax error. The other options are syntactically valid.

💻 Command Output

advanced

Output when iterating over array with unquoted expansion

What is the output of this script?

Bash Scripting

arr=("one two" three)
for i in ${arr[@]}; do
  echo "$i"
done

A

one two
three

B

one
two
three

C one two three

D Syntax error

💡 Hint

Unquoted expansion splits elements on spaces.

Without quotes, each element is split by spaces, so 'one two' becomes two words.

🚀 Application

expert

Count total words from all array elements in bash

Given an array with elements containing multiple words, which script correctly counts the total number of words across all elements?

Bash Scripting

arr=("hello world" "foo bar baz" "single")

A

count=0
for i in "${arr[@]}"; do
  count=$((count + $(echo "$i" | wc -w)))
done
 echo $count

B

count=0
for i in "${arr[@]}"; do
  count=$((count + 1))
done
 echo $count

C

count=0
for i in ${arr[@]}; do
  count=$((count + 1))
done
 echo $count

D

count=0
for i in ${arr[@]}; do
  count=$((count + $(echo "$i" | wc -w)))
done
 echo $count

💡 Hint

Use quotes to preserve elements and count words inside each element.

Option A correctly iterates over each element as a whole string and counts words inside it, summing them up.

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