Solidity Scripting

Introduction

Solidity scripting is a way to declaratively deploy contracts using Solidity, instead of using the more limiting and less user friendly forge create.

Solidity scripts are like the scripts you write when working with tools like Hardhat; what makes Solidity scripting different is that they are written in Solidity instead of JavaScript, and they are run on the fast Foundry EVM backend, which provides dry-run capabilities.

Set Up

Let’s try to deploy the NFT contract made in the solmate tutorial with solidity scripting. First of all, we would need to create a new Foundry project via:

forge init solidity-scripting

Since the NFT contract from the solmate tutorial inherits both solmate and OpenZeppelin contracts, we’ll have to install them as dependencies by running:

# Enter the project
cd solidity-scripting

# Install Solmate and OpenZeppelin contracts as dependencies
forge install transmissions11/solmate Openzeppelin/openzeppelin-contracts

Next, we have to delete the Counter.sol file in the src folder and create another file called NFT.sol. You can do this by running:

rm src/Counter.sol test/Counter.t.sol && touch src/NFT.sol && ls src

set up commands

Once that’s done, you should open up your preferred code editor and copy the code below into the NFT.sol file.

// SPDX-License-Identifier: UNLICENSED
pragma solidity >=0.8.10;

import "solmate/tokens/ERC721.sol";
import "openzeppelin-contracts/contracts/utils/Strings.sol";
import "openzeppelin-contracts/contracts/access/Ownable.sol";

error MintPriceNotPaid();
error MaxSupply();
error NonExistentTokenURI();
error WithdrawTransfer();

contract NFT is ERC721, Ownable {

    using Strings for uint256;
    string public baseURI;
    uint256 public currentTokenId;
    uint256 public constant TOTAL_SUPPLY = 10_000;
    uint256 public constant MINT_PRICE = 0.08 ether;

    constructor(
        string memory _name,
        string memory _symbol,
        string memory _baseURI
    ) ERC721(_name, _symbol) {
        baseURI = _baseURI;
    }

    function mintTo(address recipient) public payable returns (uint256) {
        if (msg.value != MINT_PRICE) {
            revert MintPriceNotPaid();
        }
        uint256 newTokenId = ++currentTokenId;
        if (newTokenId > TOTAL_SUPPLY) {
            revert MaxSupply();
        }
        _safeMint(recipient, newTokenId);
        return newTokenId;
    }

    function tokenURI(uint256 tokenId)
        public
        view
        virtual
        override
        returns (string memory)
    {
        if (ownerOf(tokenId) == address(0)) {
            revert NonExistentTokenURI();
        }
        return
            bytes(baseURI).length > 0
                ? string(abi.encodePacked(baseURI, tokenId.toString()))
                : "";
    }

    function withdrawPayments(address payable payee) external onlyOwner {
        uint256 balance = address(this).balance;
        (bool transferTx, ) = payee.call{value: balance}("");
        if (!transferTx) {
            revert WithdrawTransfer();
        }
    }
}

Now, let’s try compiling our contract to make sure everything is in order.

forge build

If your output looks like this, the contracts successfully compiled. compile successful

Deploying our contract

We’re going to deploy the NFT contract to the Rinkeby testnet, but to do this we’ll need to configure Foundry a bit, by setting things like a Rinkeby RPC URL, the private key of an account that’s funded with Rinkeby Eth, and an Etherscan key for the verification of the NFT contract.

💡 Note: You can get some Rinkeby testnet ETH here .

Environment Configuration

Once you have all that create a .env file and add the variables. Foundry automatically loads in a .env file present in your project directory.

The .env file should follow this format:

RINKEBY_RPC_URL=
PRIVATE_KEY=
ETHERSCAN_KEY=

We now need to edit the foundry.toml file. There should already be one in the root of the project.

Add the following lines to the end of the file:

[rpc_endpoints]
rinkeby = "${RINKEBY_RPC_URL}"

[etherscan]
rinkeby = { key = "${ETHERSCAN_KEY}" }

This creates a RPC alias for Rinkeby and loads the Etherscan API key.

Writing the Script

Next, we have to create a folder and name it script and create a file in it called NFT.s.sol. This is where we will create the deployment script itself.

The contents of NFT.s.sol should look like this:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "forge-std/Script.sol";
import "../src/NFT.sol";

contract MyScript is Script {
    function run() external {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        vm.startBroadcast(deployerPrivateKey);

        NFT nft = new NFT("NFT_tutorial", "TUT", "baseUri");

        vm.stopBroadcast();
    }
}

Now let’s read through the code and figure out what it actually means and does.

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

Remember even if it’s a script it still works like a smart contract, but is never deployed, so just like any other smart contract written in Solidity the pragma version has to be specified.

import "forge-std/Script.sol";
import "../src/NFT.sol";

Just like we may import Forge Std to get testing utilities when writing tests, Forge Std also provides some scripting utilities that we import here.

The next line just imports the NFT contract.

contract MyScript is Script {

We create a contract called MyScript and it inherits Script from Forge Std.

 function run() external {

By default, scripts are executed by calling the function named run, our entrypoint.

uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");

This loads in the private key from our .env file. Note: you must be careful when exposing private keys in a .env file and loading them into programs. This is only recommended for use with non-priviliged deployers or for local / test setups. For production setups please review the various wallet options that Foundry supports.

vm.startBroadcast(deployerPrivateKey);

This is a special cheatcode that records calls and contract creations made by our main script contract. We pass the deployerPrivateKey in order to instruct it to use that key for signing the transactions. Later, we will broadcast these transactions to deploy our NFT contract.

 NFT nft = new NFT("NFT_tutorial", "TUT", "baseUri");

Here we just create our NFT contract. Because we called vm.startBroadcast() before this line, the contract creation will be recorded by Forge, and as mentioned previously, we can broadcast the transaction to deploy the contract on-chain. The broadcast transaction logs will be stored in the broadcast directory by default. You can change the logs location by setting broadcast in your foundry.toml file.

Now that you’re up to speed about what the script smart contract does, let’s run it.

You should have added the variables we mentioned earlier to the .env for this next part to work.

At the root of the project run:

# To load the variables in the .env file
source .env

# To deploy and verify our contract
forge script script/NFT.s.sol:MyScript --rpc-url $RINKEBY_RPC_URL --broadcast --verify -vvvv

Forge is going to run our script and broadcast the transactions for us - this can take a little while, since Forge will also wait for the transaction receipts. You should see something like this after a minute or so:

contract verified

This confirms that you have successfully deployed the NFT contract to the Rinkeby testnet and have also verified it on Etherscan, all with one command.

Deploying locally

You can deploy to Anvil, the local testnet, by configuring the port as the fork-url.

Here, we have two options in terms of accounts. We can either start anvil without any flags and use one of the private keys provided. Or, we can pass a mnemonic to anvil to use.

Using Anvil's Default Accounts

First, start Anvil:

anvil

Update your .env file with a private key given to you by Anvil.

Then run the following script:

forge script script/NFT.s.sol:MyScript --fork-url http://localhost:8545 --broadcast

Using a Custom Mnemonic

Add the following line to your .env file and complete it with your mnemonic:

MNEMONIC=

It is expected that the PRIVATE_KEY environment variable we set earlier is one of the first 10 accounts in this mnemonic.

Start Anvil with the custom mnemonic:

source .env

anvil --m $MNEMONIC

Then run the following script:

forge script script/NFT.s.sol:MyScript --fork-url http://localhost:8545 --broadcast

💡 Note: A full implementation of this tutorial can be found here and for further reading about solidity scripting, you can check out the forge script reference.