Simulated UPI Payment Interface

mock-pay.md

Mock Pay — Simulated UPI Payment in Bash

⏱ Duration: 30 minutes

🧪 Concepts: Functions, Arrays, CLI Arguments, Input Validation, Shell UX

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🎯 Objective

Simulate a UPI-style payment system using a Bash script that:

• Accepts the receiver’s name and amount as arguments
• Displays a list of popular payment methods (e.g., GPay, PhonePe, etc.)
• Prompts the user to select one
• Uses functions, arrays, and case logic to simulate payment processing
• Displays a confirmation message with emoji ✨

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🛠 How to Use

1. Make the script executable:

   chmod +x mock_pay.sh

2. Run the script with receiver name and amount:

   ./mock_pay.sh Ravi 250

3. Follow the on-screen instructions to pick a payment method.

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💡 Sample Output

👋 Welcome to Mock UPI Bash App!
Paying ₹250 to: Ravi
🧾 Available Payment Methods:
1. PhonePe
2. GPay
3. Paytm
4. AmazonPay
5. BHIM UPI
💳 Choose a payment method [1-5]: 2
🔐 Initiating payment of ₹250 to Ravi via GPay...
⌛ Processing...
✅ Payment Successful! Thank you for using GPay 🙏

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🧠 Concepts Covered

Feature	Purpose
declare -a	Store multiple payment methods in array
$1, $2	Accept command-line arguments
functions	Encapsulate logic like simulate_payment()
read -p	User input for method choice
case, if	Validate and branch logic
sleep	Simulate real-time delay in response

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💎 Bonus Challenges (For Enthusiasts)

• Add fake UPI ID entry + OTP screen using $RANDOM
• Introduce a 10% random chance of “Transaction Failed ❌”
• Log all successful payments to a transactions.log file
• Add difficulty levels: prepaid wallet, credit card, UPI

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🏁 Why This Exercise?

Because it's fun, contextual (India-based UPI), and teaches real scripting concepts:

• CLI apps
• Argument parsing
• User interaction
• Basic stateful logic

“This is how we teach core scripting — with real-life stuff students already use daily.” 🇮🇳

mock_pay.sh

#!/bin/bash
# mock_pay.sh — Simulated UPI Payment CLI App

declare -a methods=("PhonePe" "GPay" "Paytm" "AmazonPay" "BHIM UPI")

# Function to show available methods
show_methods() {
  echo "🧾 Available Payment Methods:"
  for i in "${!methods[@]}"; do
    echo "$((i+1)). ${methods[$i]}"
  done
}

# Function to simulate payment
simulate_payment() {
  name="$1"
  amount="$2"
  method="$3"

  echo "🔐 Initiating payment of ₹$amount to $name via $method..."
  sleep 1
  echo "⌛ Processing..."
  sleep 1
  echo "✅ Payment Successful! Thank you for using $method 🙏"
}

# Input validation
if [ $# -lt 2 ]; then
  echo "Usage: $0 <ReceiverName> <Amount>"
  exit 1
fi

receiver="$1"
amount="$2"

echo "👋 Welcome to Mock UPI Bash App!"
echo "Paying ₹$amount to: $receiver"

# Show and choose method
show_methods
read -p "💳 Choose a payment method [1-${#methods[@]}]: " choice

if ! [[ "$choice" =~ ^[1-5]$ ]]; then
  echo "❌ Invalid choice. Exiting."
  exit 1
fi

selected_method="${methods[$((choice-1))]}"
simulate_payment "$receiver" "$amount" "$selected_method"