Iterating over arrays in Bash Scripting - Mini Project: Build & Apply

Iterating over arrays

📖 Scenario: You are managing a list of fruits in a small fruit shop. You want to write a script that goes through each fruit in your list and shows it on the screen.

🎯 Goal: Build a Bash script that creates an array of fruits, sets up a counter, loops through the array to print each fruit with its number, and finally displays all the fruits one by one.

📋 What You'll Learn

Create an array called fruits with the exact values: Apple, Banana, Cherry, Date, Elderberry

Create a variable called count and set it to 1

Use a for loop with the variable fruit to iterate over the fruits array

Inside the loop, print the current count and fruit, then increase count by 1

Print each fruit on its own line as the final output

💡 Why This Matters

🌍 Real World

Automating tasks like listing items, processing lists of files, or managing simple inventories.

💼 Career

Basic scripting skills like looping over arrays are essential for system administrators, DevOps engineers, and anyone working with automation.

1

Create the fruits array

Create an array called fruits with these exact values: Apple, Banana, Cherry, Date, Elderberry.

Bash Scripting

# Create the fruits array
# Your code here

Hint

Use parentheses () to create an array in Bash.

2

Set up the counter

Create a variable called count and set it to 1.

Bash Scripting

fruits=(Apple Banana Cherry Date Elderberry)
# Create a variable called count and set it to 1
# Your code here

Hint

Just write count=1 to start counting from one.

3

Loop through the fruits array

Use a for loop with the variable fruit to iterate over the fruits array. Inside the loop, print the current count and fruit, then increase count by 1.

Bash Scripting

fruits=(Apple Banana Cherry Date Elderberry)
count=1
# Use a for loop with fruit to iterate over fruits
# Inside the loop, print count and fruit, then increase count
# Your code here

Hint

Use for fruit in "${fruits[@]}" to loop over all fruits.

4

Print the final output

Run the script to print each fruit with its number on its own line.

Bash Scripting

fruits=(Apple Banana Cherry Date Elderberry)
count=1
for fruit in "${fruits[@]}"; do
    echo "$count. $fruit"
    ((count++))
done
# Run the script to print the fruits
# Your code here

Hint

Just run the script. The echo inside the loop prints each fruit with its number.

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