Deploy a Smart Contract with Foundry

Deploying a Contract Using Foundry

This tutorial will walk you through writing and compiling an ERC-20 Solidity smart contract. You'll then deploy and interact with it on the Hedera network using the Hedera Smart Contract Service (HSCS) and Foundry, connecting via the JSON-RPC relay.

What you will accomplish

By the end of this tutorial, you will be able to:

• Compile and deploy a smart contract using Foundry

• Interact with a smart contract using Foundry's cast command

• Verify your smart contract on Hashscan

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Prerequisites

Before you begin, you should have completed the following tutorial:

• Create and Fund a Testnet Account via the Hedera Faucet

• Install Foundry

curl -L https://foundry.paradigm.xyz | bash
foundryup

This will install forge, cast, anvil, and chisel.

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Table of Contents

1. Step 1: Project Setup

2. Step 2: Creating the ERC20 Contract

3. Step 3: Create a Deployment Script

4. Step 4: Deploy your ERC20 Smart Contract

5. Step 5: Interacting with the Contract

6. Step 6: Verifying the Contract on Hashscan

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Step 1: Project Setup

Initialize Project

Set up your Foundry project:

forge init hedera-foundry-erc20-tutorial
cd hedera-foundry-erc20-tutorial

This creates a new directory with a standard Foundry project structure, including src, test, and script folders.

Install Dependencies

Foundry uses git submodules to manage dependencies. We'll install the OpenZeppelin Contracts library, which provides a standard and secure implementation of the ERC20 token.

forge install OpenZeppelin/openzeppelin-contracts

This command will download the contracts and add them to your lib folder.

Create .env File

Create a `.env` file in your project's root directory to securely store your private key and the RPC URL for the Hedera Testnet.

touch .env

Securely store your sensitive data like the OPERATOR_KEY in a .env file. For the JSON RPC_URL, we'll use the Hashio RPC endpoint for testnet.

.env

OPERATOR_KEY=your-operator-key
RPC_URL=https://testnet.hashio.io/api

Replace the your-operator-key environment variable with the HEX Encoded Private Key for your ECDSA account from the Hedera Portal.

Please note: that Hashio is intended for development and testing purposes only. For production use cases, it's recommended to use commercial-grade JSON-RPC Relay or host your own instance of the Hiero JSON-RPC Relay.

Configure Foundry

Foundry uses the foundry.toml file for configuration. Open it and add profiles for the Hedera Testnet RPC endpoint.

foundry.toml

[profile.default]
src = "src"
out = "out"
libs = ["lib"]

# Add this section for Hedera Testnet
[rpc_endpoints]
testnet = "${RPC_URL}"

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Step 2: Creating the ERC20 Contract

Create a new Solidity file (HederaToken.sol ) inside the src directory:

src/HederaToken.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.22;

import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";

contract HederaToken is ERC20, Ownable {
    constructor(address initialOwner)
        ERC20("HederaToken", "HEDT")
        Ownable(initialOwner)
    {
        _mint(msg.sender, 1000 * 10 ** decimals());
    }

    function mint(address to, uint256 amount) public onlyOwner {
        _mint(to, amount);
    }
}

The contract uses the OpenZeppelin ERC20 and Ownable implementations.

• The token is named "HederaToken" with the symbol "HEDT"

• The constructor mints an initial supply of 1,000 tokens to the deployer of the contract

• An onlyOwner mint function is included to allow the contract owner to mint more tokens in the future.

Now, compile the contract:

forge build

This command compiles your contracts and places the artifacts(including the ABI and bytecode) into the out directory. We are now ready to deploy the smart contract.

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Step 3: Create a Deployment Script

Using a script is the standard and most reliable way to handle deployments in Foundry. Create a new file named HederaToken.s.sol inside the script directory.

script/HederaToken.s.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.22;

import {Script, console} from "forge-std/Script.sol";
import {HederaToken} from "../src/HederaToken.sol";

contract HederaTokenScript is Script {
    function run() external returns (address) {
        // Load the private key from the .env file
        uint256 deployerPrivateKey = vm.envUint("OPERATOR_KEY");
        
        // Start broadcasting transactions with the loaded private key
        vm.startBroadcast(deployerPrivateKey);

        // Get the deployer's address to use as the initial owner
        address deployerAddress = vm.addr(deployerPrivateKey);

        // Deploy the contract
        HederaToken hederaToken = new HederaToken(deployerAddress);

        // Stop broadcasting
        vm.stopBroadcast();

        console.log("HederaToken deployed to:", address(hederaToken));

        return address(hederaToken);
    }
}

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Step 4: Deploy Your ERC20 Smart Contract

Now, execute the script to deploy your contract. Foundry will automatically load the variables from your .env file.

forge script script/HederaToken.s.sol:HederaTokenScript --rpc-url testnet --broadcast

After a few moments, you will see the address of your newly deployed contract:

[⠒] Compiling...
[⠒] Sending transaction...
[⠒] Waiting for receipt...
== Logs ==
  HederaToken deployed to: 0x047f8c7569b9beecab790902ba29daad143041d7

Copy the deployed contract address—you'll need this in subsequent steps.

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Step 5: Interacting with the Contract

Now that the contract is deployed, you can interact with it using cast, Foundry's command-line tool for making RPC calls.

To use cast and other command-line tools, you need to load the variables from your .env file into your current terminal session.

Load Environment Variables

Run the following command to load the OPERATOR_KEY and RPC_URL into your shell:

source .env

Now your shell knows the value of $OPERATOR_KEY and $RPC_URL.

Set Up Shell Variables

Next, set up variables for your contract address and public address to make the next commands easier to read. Please export these variables in your shell.

# Replace with the contract address from the previous step
export CONTRACT_ADDRESS=<your-contract-address>

# Derive your public address from the private key
export MY_ADDRESS=$(cast wallet address $OPERATOR_KEY)

Check Your Balance

Let's call the balanceOf function to check the token balance of your account.

cast call $CONTRACT_ADDRESS "balanceOf(address)" $MY_ADDRESS --rpc-url $RPC_URL

The output will be the balance in its raw form (with 18 decimals):

0x00000000000000000000000000000000000000000000003635c9adc5dea00000

You can use the following to convert the hexadecimal to a decimal number so it's human readable.

cast --to-dec 0x00000000000000000000000000000000000000000000003635c9adc5dea00000

You should see the value 1000000000000000000000.

Transfer Tokens

Next, let's transfer 100 tokens to a new account. For this example, we'll generate a new random private key.

# Generate a new random private key and get its address
export RECIPIENT_ADDRESS=$(cast wallet address $(openssl rand -hex 32))
echo "Recipient Address: $RECIPIENT_ADDRESS"

Now, send 100 tokens to this new address. Note that 100e18 is a convenient way to write 100 * 10^18.

cast send $CONTRACT_ADDRESS "transfer(address,uint256)" $RECIPIENT_ADDRESS 100e18 \
    --private-key $OPERATOR_KEY \
    --rpc-url $RPC_URL

After the transaction confirms, check the recipient's balance:

cast call $CONTRACT_ADDRESS "balanceOf(address)" $RECIPIENT_ADDRESS --rpc-url testnet

The output will show the 100 tokens you sent:

0x0000000000000000000000000000000000000000000000056bc75e2d63100000

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Step 6: Verifying the Contract on Hashscan

Verifying your smart contract makes its source code publicly available on Hashscan. The constructor for this contract takes one argument (initialOwner), which we must provide for successful verification.

Run the following command, using the variables you set earlier.

forge verify-contract $CONTRACT_ADDRESS src/HederaToken.sol:HederaToken \
    --chain-id 296 \
    --verifier sourcify \
    --verifier-url "https://server-verify.hashscan.io/" \
    --constructor-args $(cast abi-encode "constructor(address)" $MY_ADDRESS)

After running the command, you should see a success message.

Submitting verification for [HederaToken] "0x047F8c7569B9beECaB790902BA29DaAD143041d7". 
Contract successfully verified

Congratulations! 🎉 You have successfully deployed, interacted with, and verified an ERC20 smart contract on the Hedera Testnet using Foundry. Feel free to reach out in Discord!

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Next Steps

• Check out OpenZeppelin ERC-20 Documentation

• See the full code in the Hedera-Code-Snippets Repository