Hello Scheduled World

A hands-on tutorial showcasing Hedera's on-chain cron jobs!

On traditional EVM chains, smart contracts cannot "wake up" on their own. Hedera changes this. With HSS (HIP-1215), contracts can schedule future calls to themselves—no off-chain bots required!

What's Inside

Contract	Purpose	Complexity
HelloScheduledWorld.sol	Simple scheduled messages	⭐ Minimal (~50 lines)
HelloScheduledAirdrop.sol	ERC20 with scheduled airdrops	⭐⭐⭐ Advanced

Quick Start

Prerequisites

• Foundry installed
• Hedera Testnet account from portal.hedera.com

Setup

# Clone & setup
git clone https://github.com/hedera-dev/devday-tutorial-hello-scheduled-world.git
cd devday-tutorial-hello-scheduled-world
forge install
cp .env.example .env
# Edit .env with your HEDERA_PRIVATE_KEY

# Load environment variables
source .env

HelloScheduledWorld (Simple)

# Deploy with 5 HBAR funding
forge create src/HelloScheduledWorld.sol:HelloScheduledWorld \
  --rpc-url $HEDERA_RPC_URL \
  --broadcast \
  --private-key $HEDERA_PRIVATE_KEY \
  --value 5ether

# Save the deployed address
export CONTRACT_ADDRESS=0x...

# Start scheduling "Hello Hedera!" every 15 seconds
cast send $CONTRACT_ADDRESS \
  'scheduleMessage(string,uint256)' 'Hello Hedera!' 15 \
  --rpc-url $HEDERA_RPC_URL \
  --private-key $HEDERA_PRIVATE_KEY

# Watch events on HashScan
# https://hashscan.io/testnet/contract/<CONTRACT_ADDRESS>

# Stop scheduling
cast send $CONTRACT_ADDRESS \
  'stopScheduling()' \
  --rpc-url $HEDERA_RPC_URL \
  --private-key $HEDERA_PRIVATE_KEY

HelloScheduledAirdrop (Advanced)

# Deploy with 10 HBAR funding (name, symbol, initial supply)
forge create src/HelloScheduledAirdrop.sol:HelloScheduledAirdrop \
  --rpc-url $HEDERA_RPC_URL \
  --broadcast \
  --private-key $HEDERA_PRIVATE_KEY \
  --value 10ether \
  --constructor-args "Airdrop Token" "ADT" 1000000000000000000000000

# Save the deployed address
export TOKEN_ADDRESS=0x...

# Register for airdrop
cast send $TOKEN_ADDRESS \
  'registerForAirdrop()' \
  --rpc-url $HEDERA_RPC_URL \
  --private-key $HEDERA_PRIVATE_KEY

# Start airdrop (100 tokens, every 20 seconds, 5 drops max)
cast send $TOKEN_ADDRESS \
  'startAirdrop(uint256,uint256,uint256,string)' \
  100000000000000000000 20 5 'Congrats on your airdrop!' \
  --rpc-url $HEDERA_RPC_URL \
  --private-key $HEDERA_PRIVATE_KEY

# Check status
cast call $TOKEN_ADDRESS 'getStatus()' --rpc-url $HEDERA_RPC_URL

# Stop airdrop
cast send $TOKEN_ADDRESS \
  'stopAirdrop()' \
  --rpc-url $HEDERA_RPC_URL \
  --private-key $HEDERA_PRIVATE_KEY

Running Tests

# Run all tests
forge test

# Run with verbosity
forge test -vvv

# Run specific test file
forge test --match-path test/HelloScheduledWorld.t.sol -vvv
forge test --match-path test/HelloScheduledAirdrop.t.sol -vvv

# Run specific test function
forge test --match-test test_Register -vvv

Documentation

• docs/GUIDE.md - Step-by-step tutorial (start here!)
• docs/HOW_IT_WORKS.md - Technical deep-dive

Resources

• HIP-1215 - Generalized Scheduled Contract Calls
• Hedera Portal - Get testnet account
• HashScan - Block explorer

License

MIT