How to loop through an array of strings in Bash?

To loop through an array of strings in Bash, use a for loop with the array’s elements expanded using "${array[@]}". Here’s how:

Basic Loop Through Array Elements

# Declare an array
fruits=("apple" "banana" "cherry" "date")

# Loop through each element
for fruit in "${fruits[@]}"; do
  echo "Fruit: $fruit"
done

Output:

Fruit: apple
Fruit: banana
Fruit: cherry
Fruit: date

Loop with Indexes

Iterate using the array’s indices (e.g., for modifying elements):

for i in "${!fruits[@]}"; do
  echo "Index $i: ${fruits[$i]}"
done

Output:

Index 0: apple
Index 1: banana
Index 2: cherry
Index 3: date

Key Notes

1. Syntax:

• "${array[@]}": Expands to all elements (preserves spaces in elements).
• "${!array[@]}": Expands to all indices (useful for indexed loops).
• Always quote "${array[@]}" to handle spaces/special characters correctly.

1. Avoid "${array[*]}"
"${array[*]}" merges elements into a single string (usually not desired).

Example with Spaces in Elements

# Array with elements containing spaces
items=("first item" "second item" "third item")

for item in "${items[@]}"; do
  echo "Item: $item"
done

Output:

Item: first item
Item: second item
Item: third item

Modifying Array Elements

Update elements while looping (using index-based loop):

for i in "${!fruits[@]}"; do
  fruits[$i]="${fruits[$i]} pie"  # Append " pie" to each element
done

echo "${fruits[@]}"  # Output: apple pie banana pie cherry pie date pie

Common Pitfalls

• Forgetting Quotes:
  for fruit in ${fruits[@]} → Fails if elements contain spaces.
• Using * Instead of @:
  for fruit in "${fruits[*]}" → Treats the entire array as a single string.

Summary

• Basic Loop:
  for element in "${array[@]}"; do ... done
• Index-Based Loop:
  for i in "${!array[@]}"; do ... done
• Always Quote "${array[@]}" to handle spaces and special characters.