Bash Script to Find Sum of Even Numbers

Use a Bash script that loops through numbers, checks if each number is even with if (( num % 2 == 0 )), and adds it to a sum variable; for example: sum=0; for num in {1..10}; do if (( num % 2 == 0 )); then ((sum+=num)); fi; done; echo $sum.

Examples

Input1 2 3 4 5

Output6

Input10 15 20 25 30

Output60

Input1 3 5 7

Output0

How to Think About It

To find the sum of even numbers, go through each number one by one, check if it divides evenly by 2 using the remainder operator %, and if yes, add it to a running total. This way, you only add even numbers and ignore odd ones.

Algorithm

1

Initialize a sum variable to zero.

2

Loop through each number in the given list or range.

3

Check if the current number is even by using the remainder operator.

4

If it is even, add it to the sum.

5

After the loop ends, output the sum.

Code

bash

sum=0
for num in "$@"; do
  if (( num % 2 == 0 )); then
    ((sum+=num))
  fi
done
echo "$sum"

Output

6

Dry Run

Let's trace the input '1 2 3 4 5' through the code

1

Initialize sum

sum=0

2

Check number 1

1 % 2 = 1 (odd), sum remains 0

3

Check number 2

2 % 2 = 0 (even), sum = 0 + 2 = 2

4

Check number 3

3 % 2 = 1 (odd), sum remains 2

5

Check number 4

4 % 2 = 0 (even), sum = 2 + 4 = 6

6

Check number 5

5 % 2 = 1 (odd), sum remains 6

7

Output sum

Print 6

Number	Is Even?	Sum After Step
1	No	0
2	Yes	2
3	No	2
4	Yes	6
5	No	6

Why This Works

Step 1: Check even numbers

The script uses num % 2 == 0 to find even numbers because even numbers have no remainder when divided by 2.

Step 2: Add to sum

When a number is even, it is added to the sum variable using ((sum+=num)) which updates the total.

Step 3: Output result

After checking all numbers, the script prints the total sum of even numbers with echo.

Alternative Approaches

Using seq and awk

bash

seq 1 10 | awk '{if ($1 % 2 == 0) sum += $1} END {print sum}'

This uses external tools and is concise but less flexible for input arguments.

Using while loop and read

bash

sum=0
while read num; do
  if (( num % 2 == 0 )); then
    ((sum+=num))
  fi
done
echo "$sum"

Reads numbers from standard input line by line; useful for piped input.

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

Time Complexity

The script loops through each number once, so the time grows linearly with the number of inputs.

Space Complexity

Only a few variables are used regardless of input size, so space usage is constant.

Which Approach is Fastest?

The pure Bash loop is efficient and simple; using external tools like awk adds overhead but can be more concise.

Approach	Time	Space	Best For
Bash loop with arithmetic	O(n)	O(1)	Simple scripts with input arguments
seq with awk	O(n)	O(1)	Quick one-liners with piped input
while read loop	O(n)	O(1)	Reading from standard input or files