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Interact with Ethereum using Foundry

Last modified: 2025-03-28

Foundry is a blazing fast, portable and modular toolkit for Ethereum application development written in Rust.

Setup Foundry

Please refer to the Foundry's repository for details.
To install foundryup, run the following command to install foundry toolchain.

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

We can set the environment variable for Ethereum RPC URL to interact the Ethereum blockchain so that we don’t need to set the RPC url flag when running each command.

export ETH_RPC_URL="http://10.0.0.1:12345/path/to/rpc"

Investigating a Chain

cast command of Foundry performs Ethereum RPC calls.

# Get the Ethereum chain id
cast chain-id
# Get the symbolic name of the current chain
cast chain
# Get the current client version
cast client

# Get the current gas price
cast gas-price

# Get the latest block number
cast block-number
# Get information about a block
cast block

Investigating Account

# Get the balance of an account in wei
cast balance <account_address or ens_name>
cast balance 0x123...
cast balance beer.eth

Investigating Contract

# Get the source code of a contract from Etherscan
cast source <contract_address> -e <etherscan_api_key>

Call Functions

If we know the functions of a target contract, we can simply call them. Note that these command do NOT send transactions, so cannot change states or values in the contract.

cast call --private-key <private_key_addr> <contract_addr> "getFlag()(string memory)"

cast call --private-key <private_key_addr> <contract_addr> "isSolved()(bool)"

Send Transactions

We can interact with the contract that is already deployed in Ethereum chain if we have the private key of the account and the contract address.

# Call the function of the contract
cast send --private-key <private_key_addr> <contract_addr> "exampleFunc(uint256)" <argument_value_of_the_function>
cast send --private-key 0x123... 0xabc... "deposit(uint256)" 10

# Trigger the fallback function
# Call the nonexisting function e.g. "dummy"
cast send --private-key <private_key_addr> <contract_addr> "dummy()"
cast send --private-key 0x123... 0xabc... "dummy()"

# Trigger the receive function
# Send Ether to call the receive function
cast send --private-key <private_key_addr> <contract_addr> --value 10gwei
cast send --private-key 0x123... 0xabc... --value 10gwei

If we got error like unsupported feature: eip1559 , add --legacy flag for the command.

References