wesyao/ethereum-hello-world-tutorial

A simple solidity smart contract

Hello World Truffle Tutorial

1. install dependencies

npm i -g ethereumjs-testrpc
npm i -g truffle

2. init truffle project

truffle init

3. write solidity Helloworld.sol contract

pragma solidity ^0.4.4;

contract Helloworld {
    string _greeting;

    function setGreeting(string greeting) {
        _greeting = greeting;
    }

    function sayHello() returns(string) {
        return _greeting;
    }
}

4. write 2_deploy_contracts.js migration script

var Helloworld = artifacts.require("./Helloworld.sol");

module.exports = function(deployer) {
  deployer.deploy(Helloworld);
};

5. open up new terminal and run testrpc

testrpc

6. build solidity smart contract

truffle build

7. migrate Helloworld smart contract

truffle migrate

8. test smart contract on truffle console

truffle console
/* console opens */
var hw;
Helloworld.deployed().then(function(d){hw = d;});
hw.sayHello.call() // ''
hw.setGreeting("hi github!");
hw.sayHello.call() // 'hi github!'

9. change sayHello on Helloworld contract

function sayHello() returns(string) {
    return "im changed!";
}

10. compile and migrate updated contract.. then run console

truffle compile
truffle migrate
/* deployed contract */
truffle console

11. run sayHello

Notice sayHello output did not change. That is because contracts are cannot be changed once deployed to the blockchain.

var hw;
Helloworld.deployed().then(function(d){hw = d;});
hw.sayHello.call() // 'hi github!'