Adding and removing elements in Bash Scripting - Step-by-Step Execution

Concept Flow - Adding and removing elements

Start with empty array

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Add element: array+=("new_element")

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Array updated with new element

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Remove element: unset 'array[index

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Array updated with element removed

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End with modified array

Start with an array, add elements using +=, remove elements using unset, then end with the updated array.

Execution Sample

Bash Scripting

arr=()
arr+=("apple")
arr+=("banana")
unset 'arr[0]'
echo "${arr[@]}"

This script adds 'apple' and 'banana' to an array, removes the first element, then prints the remaining elements.

Execution Table

Step	Command	Array State	Output
1	arr=()	[]
2	arr+=("apple")	["apple"]
3	arr+=("banana")	["apple", "banana"]
4	unset 'arr[0]'	["banana"] (index 1)
5	echo "${arr[@]}"	["banana"] (index 1)	banana

💡 After unset 'arr[0]', index 0 is removed (sparse array), remaining element at index 1; echo "${arr[@]}" prints set elements only.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
arr	[]	["apple"]	["apple", "banana"]	["banana"]	["banana"]

Key Moments - 2 Insights

What happens to indices after unset 'arr[0]'?

Index 0 is removed, 'banana' remains at index 1; indices do not shift (sparse array).

Why does echo print only 'banana'?

${arr[@]} expands to set elements only, skipping unset indices (holes).

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the array content?

A ["apple", "banana"]

B ["banana"]

C ["apple"]

D []

💡 Hint

Check the 'Array State' column at step 3 in the execution_table.

At which step is the first element removed?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Array State' after unset in step 4 in the execution_table.

If we remove 'unset' command, what will echo print at step 5?

A "banana"

B "apple banana"

C "apple"

D ""

💡 Hint

Without unset, array keeps both elements as shown in step 3.

Concept Snapshot

Bash arrays can be changed by adding elements with arr+=("value") and removing with unset 'arr[index]'.
Removing an element removes the index-value pair without shifting remaining indices (sparse array).
Use echo "${arr[@]}" to print all set elements, skipping holes.
Remember: unset does not reindex or shift the array.

Full Transcript

This lesson shows how to add and remove elements in a bash array. We start with an empty array. Then we add elements using the += operator. Next, we remove an element using unset with the element's index. Removing does not shift the array indexes, creating a sparse array (hole at index 0). When printing the array with echo and ${arr[@]}, only set elements are shown. This helps understand how bash arrays behave when modified.