Bash Script to Count Elements in Array

In Bash, you can count elements in an array using ${#array[@]}, for example: echo ${#my_array[@]} prints the number of elements.

Examples

Inputmy_array=(apple banana cherry)

Output3

Inputmy_array=()

Output0

Inputmy_array=(one)

Output1

How to Think About It

To count elements in a Bash array, you think about how Bash stores arrays and how to access their size. Bash provides a special syntax ${#array[@]} that returns the number of elements. So, you just need to use this syntax with your array variable to get the count.

Algorithm

1

Define or get the array variable.

2

Use the syntax ${#array[@]} to get the count of elements.

3

Print or return the count.

Code

bash

#!/bin/bash
my_array=(apple banana cherry)
echo "Number of elements: ${#my_array[@]}"

Output

Number of elements: 3

Dry Run

Let's trace counting elements in the array (apple banana cherry).

1

Define array

my_array=(apple banana cherry)

2

Count elements

Count = ${#my_array[@]} = 3

3

Print count

Output: Number of elements: 3

Step	Action	Value
1	Define array	my_array=(apple banana cherry)
2	Count elements	3
3	Print output	Number of elements: 3

Why This Works

Step 1: Array length syntax

The ${#array[@]} syntax returns the number of elements in the array.

Step 2: Accessing array variable

You use the array name inside the braces to get its length.

Step 3: Printing the count

Using echo prints the count to the terminal.

Alternative Approaches

Using ${#array[*]} syntax

bash

#!/bin/bash
my_array=(apple banana cherry)
echo "Count: ${#my_array[*]}"

This works the same as ${#array[@]} for counting elements but treats the array as a single word when quoted.

Using a loop to count elements

bash

#!/bin/bash
my_array=(apple banana cherry)
count=0
for element in "${my_array[@]}"; do
  ((count++))
done
echo "Count: $count"

This manually counts elements by looping, less efficient but useful if you want to process elements while counting.

Complexity: O(1) time, O(1) space

Time Complexity

Counting elements with ${#array[@]} is constant time because Bash stores the array size internally.

Space Complexity

No extra memory is needed beyond the array itself; the operation is in-place.

Which Approach is Fastest?

Using ${#array[@]} or ${#array[*]} is fastest and simplest; looping to count is slower and unnecessary.

Approach	Time	Space	Best For
${#array[@]}	O(1)	O(1)	Quick count of array elements
${#array[*]}	O(1)	O(1)	Same as above, watch quoting behavior
Loop counting	O(n)	O(1)	Counting with processing each element