#Configuration variables

A Hardhat project can use configuration variables for user-specific values or for data that shouldn't be included in the code repository.

These variables are set via tasks in the vars scope and can be retrieved in the config using the vars object. For example, if you do this in your config:

const INFURA_API_KEY = vars.get("INFURA_API_KEY");

module.exports = {
  networks: {
    sepolia: {
      url: `https://sepolia.infura.io/v3/${INFURA_API_KEY}`,
    },
  },
};

And then you set the INFURA_API_KEY with:

$ npx hardhat vars set INFURA_API_KEY
✔ Enter value: ********************************

Then the URL for the sepolia network will be formed with the configuration variable you set.

# Managing configuration variables

Use the tasks under the vars scope to manage your configuration variables.

#vars set

Assigns a value to a configuration variable, or creates one if it doesn't exist:

$ npx hardhat vars set TEST_API_KEY

#vars get

Displays a configuration variable's value:

$ npx hardhat vars get TEST_API_KEY
1234abcd1234abcd1234abcd1234abcd

#vars list

Prints all the configuration variables stored on your machine:

$ npx hardhat vars list
TEST_API_KEY
TEST_PK

#vars delete

Removes a configuration variable:

$ npx hardhat vars delete TEST_API_KEY

# Using variables in your configuration file

Configuration variables that you have previously stored can be retrieved within your Hardhat configuration file. Use the vars.get method to obtain them:

const { vars } = require("hardhat/config");

const INFURA_API_KEY = vars.get("INFURA_API_KEY");

module.exports = {
  sepolia: {
    url: `https://sepolia.infura.io/v3/${INFURA_API_KEY}`,
    accounts: [vars.get("TEST_PK")],
  },
};

For variables that may not exist, you can specify a default value as the second parameter:

const salt = vars.get("DEPLOY_SALT", "12345");

You can also use vars.has to check if a variable exists:

const accounts = vars.has("TEST_PK") ? [vars.get("TEST_PK")] : [];

# Setting up variables for a project

The vars setup task lists all the configuration variables used by the project. This is useful to know which ones you need to set up before running the project.

#Mandatory vs. optional variables

The output of vars setup separates mandatory variables from optional ones.

A variable is considered mandatory if the configuration cannot be loaded without it. This happens when you retrieve the variable without a default value:

vars.get("MANDATORY_VARIABLE");

However, when combined with vars.has, the variable is considered optional:

vars.has("OPTIONAL_VARIABLE") ? [vars.get("OPTIONAL_VARIABLE")] : [];

Variables always used with a default value are also considered optional:

vars.get("ANOTHER_OPTIONAL_VARIABLE", "DEFAULT_VALUE");

# Migrating from dotenv

If you are using dotenv, we recommend you migrate to our built-in configuration variables manager. This will make it easier to share values across various Hardhat projects, and will minimize the risk of exposing sensitive data by accidentally uploading a .env file to a public repository.

To migrate from dotenv, follow these steps:

1. Replace process.env.KEY references in your configuration with vars.get("KEY"). Replace conditions like process.env.KEY !== undefined with vars.has("KEY")
2. Run npx hardhat vars setup to identify all the variables that are used by your project.
3. Use npx hardhat vars set for each variable as indicated by the setup task.
4. After substituting all instances of process.env, you may uninstall the dotenv package and remove its import from your configuration.

# Overriding configuration variables with environment variables

Environment variables prefixed with HARDHAT_VAR_ can be used to override the values of configuration variables.

For example, if your config uses vars.get("MY_KEY") and you run Hardhat with the environment variable HARDHAT_VAR_MY_KEY set to some value, then that value is going to be used:

HARDHAT_VAR_MY_KEY=123 npx hardhat some-task

Keep in mind that changes to environment variables during the configuration execution are not recognized. For example, if you do this:

process.env.HARDHAT_VAR_MY_KEY = "123";
console.log(vars.get("MY_KEY"));

Then the value of MY_KEY won't be "123".