Bash Script to Find Area of Circle with User Input

Use a Bash script that reads the radius and calculates area with area=$(echo "scale=2; 3.1416 * $radius * $radius" | bc) to find the circle's area.

Examples

Input5

OutputArea of circle with radius 5 is 78.54

Input0

OutputArea of circle with radius 0 is 0.00

Input2.5

OutputArea of circle with radius 2.5 is 19.63

How to Think About It

To find the area of a circle, first get the radius from the user. Then multiply pi (3.1416) by the radius squared. Use a calculator tool like bc in Bash to handle decimal math.

Algorithm

1

Get the radius input from the user

2

Calculate area using formula: pi * radius * radius

3

Print the calculated area with two decimal places

Code

bash

#!/bin/bash
read -p "Enter radius: " radius
area=$(echo "scale=2; 3.1416 * $radius * $radius" | bc)
echo "Area of circle with radius $radius is $area"

Output

Enter radius: 5
Area of circle with radius 5 is 78.54

Dry Run

Let's trace radius=5 through the code

1

Input radius

User enters 5

2

Calculate area

3.1416 * 5 * 5 = 78.54

3

Print result

Output: Area of circle with radius 5 is 78.54

Step	Radius	Calculation	Area
1	5	3.1416 * 5 * 5	78.54

Why This Works

Step 1: Reading Input

The script uses read to get the radius from the user.

Step 2: Calculating Area

It uses bc with scale=2 to do decimal math for the formula pi * radius * radius.

Step 3: Displaying Output

Finally, it prints the area with the radius value for clarity.

Alternative Approaches

Using awk for calculation

bash

#!/bin/bash
read -p "Enter radius: " radius
area=$(awk "BEGIN {printf \"%.2f\", 3.1416 * $radius * $radius}")
echo "Area of circle with radius $radius is $area"

This uses awk instead of bc for floating-point math, which can be faster and simpler on some systems.

Using printf with bash arithmetic (integer only)

bash

#!/bin/bash
read -p "Enter radius (integer): " radius
area=$((3 * radius * radius / 1))
echo "Approximate area (integer) is $area"

This uses integer math only and is less precise but avoids external tools.

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

Time Complexity

The script performs a fixed number of operations regardless of input size, so it runs in constant time.

Space Complexity

It uses a few variables and no extra data structures, so space usage is constant.

Which Approach is Fastest?

Using Bash arithmetic is fastest but limited to integers; awk and bc handle decimals but add slight overhead.

Approach	Time	Space	Best For
Using bc	O(1)	O(1)	Accurate decimal calculations
Using awk	O(1)	O(1)	Simple decimal math without bc
Bash integer arithmetic	O(1)	O(1)	Fast integer-only calculations