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ffi.md

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ffi

Signature

function ffi(string[] calldata) external returns (bytes memory);

Description

Calls an arbitrary command if ffi is enabled.

It is generally advised to use this cheat code as a last resort, and to not enable it by default, as anyone who can change the tests of a project will be able to execute arbitrary commands on devices that run the tests.

Tips

  • Make sure that the output is ABI encoded
  • Make sure that the output does not include a \n newline character. (e.g in Rust use print! vs println!)
  • Remember that the script will be executed from the top-level directory of your project, not inside test
  • Make sure that the inputs array does not have empty elements. They will be handled as inputs by the script, instead of space

Examples

string[] memory inputs = new string[](3);
inputs[0] = "echo";
inputs[1] = "-n";
// ABI encoded "gm", as a string
inputs[2] = "0x00000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000002676d000000000000000000000000000000000000000000000000000000000000";

bytes memory res = vm.ffi(inputs);
string memory output = abi.decode(res, (string));
assertEq(output, "gm");