Greeting.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.4.22 <0.8.0;

contract Greeting {
    string public greeting = "hello";

    function sayHello() external view returns (string memory) {
        return greeting;
    }

    function updateGreeting(string calldata _greeting) external {
        greeting = _greeting;
    }
}