shell-calculator

#!/bin/bash
# You can add a prompt at the end of the calculator function to ask the user if they want to repeat the operation.

# Function to perform addition
addition() {
  echo "$1 + $2" | bc
}

# Function to perform subtraction
subtraction() {
  echo "$1 - $2" | bc
}

# Function to perform multiplication
multiplication() {
  echo "$1 * $2" | bc
}

# Function to perform division
division() {
  if [ "$2" -ne 0 ]; then
    echo "scale=2; $1 / $2" | bc
  else
    echo "Error: Division by zero is undefined."
  fi
}

# Function to perform modulus
modulus() {
  if [ "$2" -ne 0 ]; then
    echo "$1 % $2" | bc
  else
    echo "Error: Modulus by zero is undefined."
  fi
}

# Main calculator function
calculator() {
  echo "Calculator Menu:"
  echo "1. Addition"
  echo "2. Subtraction"
  echo "3. Multiplication"
  echo "4. Division"
  echo "5. Modulus"
  echo "6. Exit"

  read -p "Enter your choice (1-6): " choice

  case $choice in
    1)
      read -p "Enter the first number: " num1
      read -p "Enter the second number: " num2
      result=$(addition "$num1" "$num2")
      echo "Result: $result"
      ;;
    2)
      read -p "Enter the first number: " num1
      read -p "Enter the second number: " num2
      result=$(subtraction "$num1" "$num2")
      echo "Result: $result"
      ;;
    3)
      read -p "Enter the first number: " num1
      read -p "Enter the second number: " num2
      result=$(multiplication "$num1" "$num2")
      echo "Result: $result"
      ;;
    4)
      read -p "Enter the numerator: " num1
      read -p "Enter the denominator: " num2
      result=$(division "$num1" "$num2")
      echo "Result: $result"
      ;;
    5)
      read -p "Enter the dividend: " num1
      read -p "Enter the divisor: " num2
      result=$(modulus "$num1" "$num2")
      echo "Result: $result"
      ;;
    6)
      echo "Exiting the calculator. Goodbye!"
      exit 0
      ;;
    *)
      echo "Invalid choice. Please enter a number between 1 and 6."
      ;;
  esac

  # Recursive call for continuous operation
  calculator
}

# Start the calculator
calculator
```

I added a new function `modulus` for the modulus operation, and I included it in the menu. Users can choose option '5' to perform the modulus operation. The script continues to run until the user chooses to exit by entering '6'.