Iterating over arrays in Bash Scripting - Step-by-Step Execution

Concept Flow - Iterating over arrays

Define array

↓

Start loop: for each element

↓

Access current element

↓

Execute commands with element

↓

Next element?

Yes→Repeat loop

No↓

End loop

This flow shows how a bash script defines an array, then loops over each element to run commands, repeating until all elements are processed.

Execution Sample

Bash Scripting

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

This script loops over each fruit in the array and prints it.

Execution Table

Iteration	Variable fruit	Action	Output
1	apple	Print fruit	apple
2	banana	Print fruit	banana
3	cherry	Print fruit	cherry
-	-	Loop ends	All elements processed

💡 All elements in the array have been iterated, loop ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
fruit	undefined	apple	banana	cherry	cherry

Key Moments - 2 Insights

Why do we use "${arr[@]}" instead of just "${arr}" in the loop?

Using "${arr[@]}" expands to all elements separately, so the loop iterates over each item. Using "${arr}" would treat the whole array as one string, causing only one iteration. See execution_table rows 1-3 where each fruit is printed separately.

What happens if the array is empty?

The loop body does not execute at all because there are no elements to iterate. The exit_note confirms the loop ends immediately with no output.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'fruit' during iteration 2?

A apple

B cherry

C banana

D undefined

💡 Hint

Check the 'Variable fruit' column in execution_table row for iteration 2.

At which iteration does the loop stop iterating over the array?

A After iteration 2

B After iteration 3

C After iteration 1

D Never stops

💡 Hint

Look at the exit_note and the last iteration number in execution_table.

If we change the array to arr=(dog cat), how many iterations will the loop run?

A 2

B 3

C 1

D 0

💡 Hint

Refer to variable_tracker and execution_table to see how iterations relate to array length.

Concept Snapshot

Bash array iteration:
Define array: arr=(item1 item2 ...)
Loop: for var in "${arr[@]}"; do ... done
Each loop var holds one element
Use "${arr[@]}" to expand all elements
Loop ends after last element

Full Transcript

This lesson shows how to loop over arrays in bash scripting. First, you define an array with multiple items. Then, you use a for loop with "${arr[@]}" to access each element one by one. Inside the loop, you can run commands using the current element. The loop repeats until all elements are processed. Using "${arr[@]}" is important because it expands each element separately. If the array is empty, the loop does not run. The example prints each fruit in the array on its own line.