# Writing scripts with Hardhat

In this guide we will go through the steps of creating a script with Hardhat. For a general overview of using Hardhat refer to the Getting started guide.

You can write your own custom scripts that can use all of Hardhat's functionality. A classic use case is writing a deployment script for your smart contracts.

There are two ways of writing a script that accesses the Hardhat Runtime Environment.

TIP

Hardhat scripts are useful for simple things that don't take user arguments, and for integrating with external tools that aren't well suited for the Hardhat CLI, like a Node.js debugger.

If you want to automate more complex things, and receive user arguments, you can learn how to create your own tasks here.

# Hardhat CLI dependant

You can write scripts that access the Hardhat Runtime Environment's properties as global variables.

These scripts must be run through Hardhat: npx hardhat run script.js.

This makes it easy to port scripts that were developed for other tools and that inject variables into the global state.

# Standalone scripts: using Hardhat as a library

The second option leverages Hardhat's architecture to allow for more flexibility. Hardhat has been designed as a library, allowing you to get creative and build standalone CLI tools that access your development environment. This means that by simply requiring it:

const hre = require("hardhat");

You can get access to all your tasks and plugins. To run these scripts you simply go through node: node script.js.

To try this out, let's look at a fresh Hardhat project. Run npx hardhat and go through the steps to create a sample project. When you're done your project directory should look like this:

$ ls -l
total 400
-rw-r--r--    1 fzeoli  staff     195 Jul 30 15:27 hardhat.config.js
drwxr-xr-x    3 fzeoli  staff      96 Jul 30 15:27 contracts
drwxr-xr-x  502 fzeoli  staff   16064 Jul 30 15:31 node_modules
-rw-r--r--    1 fzeoli  staff  194953 Jul 30 15:31 package-lock.json
-rw-r--r--    1 fzeoli  staff     365 Jul 30 15:31 package.json
drwxr-xr-x    3 fzeoli  staff      96 Jul 30 15:27 scripts
drwxr-xr-x    3 fzeoli  staff      96 Jul 30 15:27 test

Inside scripts/ you will find sample-script.js. Read through its comments to have a better idea of what it does.

// We require the Hardhat Runtime Environment explicitly here. This is optional
// but useful for running the script in a standalone fashion through `node <script>`.
//
// When running the script with `npx hardhat run <script>` you'll find the Hardhat
// Runtime Environment's members available in the global scope.
const hre = require("hardhat");

async function main() {
  // Hardhat always runs the compile task when running scripts with its command
  // line interface.
  //
  // If this script is run directly using `node` you may want to call compile
  // manually to make sure everything is compiled
  // await hre.run('compile');

  // We get the contract to deploy
  const Greeter = await hre.ethers.getContractFactory("Greeter");
  const greeter = await Greeter.deploy("Hello, Hardhat!");

  await greeter.deployed();

  console.log("Greeter deployed to:", greeter.address);
}

// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });

Done? Before running the script with node you need to declare ethers. This is needed because Hardhat won't be injecting it on the global scope as it does when calling the run task.


 





const hre = require("hardhat");
const ethers = hre.ethers;

async function main() {
  //...
}

Now you're ready to run the script:

$ node scripts/sample-script.js
Greeter address: 0x5FbDB2315678afecb367f032d93F642f64180aa3

By accessing the Hardhat Runtime Environment at the top, you are allowed to run the script in a standalone fashion. Hardhat always runs the compile task when it's invoked via npx hardhat run, but in a standalone fashion you may want to call compile manually to make sure everything is compiled. This is done by calling hre.run('compile'). Uncomment the following line and re-run the script with node:

await hre.run("compile");
$ node scripts/sample-script.js
Greeter address: 0x5FbDB2315678afecb367f032d93F642f64180aa3

# Hardhat arguments

You can still pass arguments to Hardhat when using it as a library. This is done by setting environment variables. These are:

  • HARDHAT_NETWORK: Sets the network to connect to.

  • HARDHAT_SHOW_STACK_TRACES: Enables JavaScript stack traces of expected errors.

  • HARDHAT_VERBOSE: Enables Hardhat verbose logging.

  • HARDHAT_MAX_MEMORY: Sets the maximum amount of memory that Hardhat can use.

Last Updated: 7/7/2021, 5:26:45 PM