Bash Script to Create Simple Calculator

You can create a simple calculator in Bash by reading two numbers and an operator, then using case to perform operations like +, -, *, and /; for example: read -p "Enter first number: " a; read -p "Enter operator (+ - * /): " op; read -p "Enter second number: " b; case $op in +) echo $((a + b)) ;; -) echo $((a - b)) ;; '*') echo $((a * b)) ;; /) echo $((a / b)) ;; esac.

Examples

Input5 + 3

Output8

Input10 / 2

Output5

Input7 * 0

Output0

How to Think About It

To build a simple calculator in Bash, first get two numbers and an operator from the user. Then, use a case statement to decide which arithmetic operation to perform based on the operator. Finally, calculate and display the result.

Algorithm

1

Prompt the user to enter the first number and store it.

2

Prompt the user to enter an operator (+, -, *, /) and store it.

3

Prompt the user to enter the second number and store it.

4

Use a case statement to check the operator and perform the corresponding arithmetic operation.

5

Print the result of the calculation.

Code

bash

read -p "Enter first number: " a
read -p "Enter operator (+ - * /): " op
read -p "Enter second number: " b
case $op in
  +) result=$((a + b)) ;;
  -) result=$((a - b)) ;;
  '*') result=$((a * b)) ;;
  /) 
    if [ "$b" -eq 0 ]; then
      echo "Error: Division by zero"
      exit 1
    fi
    result=$((a / b)) ;;
  *) echo "Invalid operator"; exit 1 ;;
esac
echo "Result: $result"

Dry Run

Let's trace the input '8 * 7' through the code

1

Read first number

a = 8

2

Read operator

op = *

3

Read second number

b = 7

4

Perform calculation

Since op is '*', calculate 8 * 7 = 56

5

Print result

Output: Result: 56

Step	Variable	Value
1	a	8
2	op	*
3	b	7
4	result	56

Why This Works

Step 1: Reading inputs

The script uses read -p to get two numbers and an operator from the user.

Step 2: Choosing operation

A case statement checks the operator and selects the correct arithmetic operation.

Step 3: Calculating and outputting

The script calculates the result using arithmetic expansion $(( )) and prints it.

Alternative Approaches

Using expr command

bash

read -p "Enter first number: " a
read -p "Enter operator (+ - \* /): " op
read -p "Enter second number: " b
result=$(expr $a $op $b)
echo "Result: $result"

Uses external expr command; less efficient but works on older shells.

Using bc for floating point

bash

read -p "Enter first number: " a
read -p "Enter operator (+ - * /): " op
read -p "Enter second number: " b
result=$(echo "$a $op $b" | bc -l)
echo "Result: $result"

Supports floating point calculations but requires bc installed.

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 O(1).

Space Complexity

It uses a few variables to store inputs and results, so space usage is constant O(1).

Which Approach is Fastest?

Using Bash arithmetic expansion is fastest and simplest; using external commands like expr or bc adds overhead.

Approach	Time	Space	Best For
Bash arithmetic expansion	O(1)	O(1)	Simple integer calculations
expr command	O(1)	O(1)	Compatibility with older shells
bc command	O(1)	O(1)	Floating point calculations