prompt.md

prompt

Signature

function prompt(string calldata promptText) external returns (string memory input);
function promptSecret(string calldata promptText) external returns (string memory input);
function promptSecretUint(string calldata promptText) external returns (uint256);

Description

Display an interactive prompt to the user for inserting arbitrary data.

vm.prompt displays an interactive input, while vm.promptSecret & vm.promptSecretUint display a hidden input, used for passwords and other secret information that should not leak to the terminal.

ℹ️ Note

This cheatcode is meant to be used in scripts ― not tests. It is also advised to follow the best practices below for testing scripts that use vm.prompt and handling timeouts, since scripts might otherwise hang or revert. This cheatcode reverts when running in a non-interactive shell.

Configuration

In order to prevent unwanted hangups, vm.prompt has a timeout configuration.

In your foundry.toml:

prompt_timeout = 120

Default value is 120 and values are in seconds.

Best practices

Testing scripts that use vm.prompt

When testing scripts containing vm.prompt it is recommended to use the following pattern:

contract Script {
    function run() public {
        uint256 myUint = vm.parseUint(vm.prompt("enter uint"));
        run(myUint);
    }

    function run(uint256 myUint) public {
        // actual logic
    }
}

That way, we are keeping the UX gain (don't have to provide --sig argument when running the script), but tests can set any value to myUint and not just a hardcoded default.

Handling timeouts

When a user fails to provide an input before the timeout expires, the vm.prompt cheatcode reverts. If you'd like, timeouts can be handled by using try/catch:

string memory input;

try vm.prompt("Username") returns (string memory res) {
    input = res;
}
catch (bytes memory) {
    input = "Anonymous";
}

Examples

Choose RPC endpoint

Provide an option to choose the RPC/chain to run on.

In your foundry.toml file:

[rpc_endpoints]
mainnet = "https://eth.llamarpc.com"
polygon = "https://polygon.llamarpc.com"

In your script:

string memory rpcEndpoint = vm.prompt("RPC endpoint");
vm.createSelectFork(rpcEndpoint);

Parse user input into native types

We can use the string parsing cheatcodes to parse the responses from users:

uint privateKey = vm.promptSecretUint("Private key");
address to = vm.parseAddress(vm.prompt("Send to"));
uint amount = vm.parseUint(vm.prompt("Amount (wei)"));
vm.broadcast(privateKey);
payable(to).transfer(amount);