Bash Script to Add Two Numbers with Output Example

Use a Bash script with read to get two numbers and sum=$((num1 + num2)) to add them, then print the result with echo.

Examples

Input3 and 5

OutputSum is 8

Input0 and 0

OutputSum is 0

Input-2 and 7

OutputSum is 5

How to Think About It

To add two numbers in Bash, first get the numbers from the user or variables, then use the arithmetic expansion $(( )) to calculate their sum, and finally print the result with echo.

Algorithm

1

Get the first number from the user

2

Get the second number from the user

3

Add the two numbers using arithmetic expansion

4

Print the sum

Code

bash

#!/bin/bash

# Ask user for first number
read -p "Enter first number: " num1

# Ask user for second number
read -p "Enter second number: " num2

# Calculate sum
sum=$((num1 + num2))

# Print the result
echo "Sum is $sum"

Output

Enter first number: 3
Enter second number: 5
Sum is 8

Dry Run

Let's trace adding 3 and 5 through the code

1

Read first number

num1 = 3

2

Read second number

num2 = 5

3

Calculate sum

sum = 3 + 5 = 8

4

Print result

Output: Sum is 8

Step	Variable	Value
1	num1	3
2	num2	5
3	sum	8

Why This Works

Step 1: Reading input

The read command waits for user input and stores it in variables num1 and num2.

Step 2: Adding numbers

The arithmetic expansion $((num1 + num2)) calculates the sum of the two numbers.

Step 3: Displaying output

The echo command prints the sum with a message to the terminal.

Alternative Approaches

Using command line arguments

bash

#!/bin/bash

num1=$1
num2=$2
sum=$((num1 + num2))
echo "Sum is $sum"

This method adds numbers passed as arguments when running the script, making it faster for automation but less interactive.

Using expr command

bash

#!/bin/bash

read -p "Enter first number: " num1
read -p "Enter second number: " num2
sum=$(expr $num1 + $num2)
echo "Sum is $sum"

Uses the older <code>expr</code> command for addition; less modern but compatible with very old shells.

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

Time Complexity

Adding two numbers is a constant time operation, so the time complexity is O(1).

Space Complexity

The script uses a fixed number of variables, so space complexity is O(1).

Which Approach is Fastest?

Using arithmetic expansion $(( )) is faster and more readable than expr and better for interactive scripts than command line arguments.

Approach	Time	Space	Best For
Arithmetic Expansion	O(1)	O(1)	Interactive scripts, readability
Command Line Arguments	O(1)	O(1)	Automation, scripting with parameters
expr Command	O(1)	O(1)	Legacy shell compatibility