"Hello World" from Solidity

How to say "Hello World" in the era of blockchain?

Reflections

Once upon a time, I worked in CTO role of a great startup, and in order to find talented code developers, we ran a competition for the most creative "Hello World" application. It was a lot of fun! I was not able to participate in the competition back then, but here is my delayed entry.

Step 1. Environment Configuration

# Installing Truffle framework (http://truffleframework.com/)
$ sudo npm install -g truffle

# Creating project
$ mkdir solidity-experiments
$ cd solidity-experiments/
$ truffle init

# Installing and starting Etherium local test network
$ sudo npm install -g ethereumjs-testrpc
$ testrpc &

Step 2. Point truffle framework to the test network

Update truffle.js file created by the init to point to your test network. File content should look like this:

module.exports = {
 networks: {
  development: {
   host: "localhost",
   port: 8545,
   network_id: "*" // Match any network id
  }
 }
};

Step 3. Create Hello.sol Solidity contract in the "/contracts" directory 

pragma solidity ^0.4.4;

contract Hello {
  function Hello() public {
    // constructor
  }

  function sayHello() public pure returns (string) {
     //console.log("sayHello() function called...");
     return 'Hello World!';
  }
}

Step 4. Create 2_deploy_contracts.js file in /migrations directory

var Hello1 = artifacts.require("./Hello.sol");

module.exports = function(deployer) {
  deployer.deploy(Hello1);
};

Step 5.  Deploy the script from truffle console 

$ truffle console

truffle(development)>  truffle migrate --reset
Using network 'development'.

Running migration: 1_initial_migration.js
  Deploying Migrations...
  ... 0xb6bbeaaf3649ecb38d548cba96f681682dad9e0225726924fbee3ce36eff94e3
  Migrations: 0xc08c46796ba0edc0bebbbd0d90868c010055cb0e
Saving successful migration to network...
  ... 0x16fe364b9f2c3e8f07fa1ebd6b84b8ad9b4e750d8698a7e920d824ebd019dd80
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Deploying Hello...
  ... 0xfe120836b2d7395bd988104feff018fe352f93555f71003bbf1a64671cca9ba1
  Hello: 0x2b649a87d20ce1ac3b6a0218e911165fa0f095f0
Saving successful migration to network...
  ... 0x1a09073a3b3f7996f3d63a81a99d8cd09198ad7b467f35f7ddc500a4291332b9
Saving artifacts...
truffle(development)>

Step 6.  Run "Hello World"

truffle(development)> var he = Hello.at(Hello.address)
undefined

truffle(development)> he.sayHello()
'Hello World!'