ethereum

Some simple steps to get started with geth.

Setting Up

Install everything you need to interact with the Ethereum blockchain:

sudo apt-get install software-properties-common
sudo add-apt-repository -y ppa:ethereum/ethereum
sudo apt-get update
sudo apt-get install ethereum solc

Create a genesis file genesis.json in the working directory. You may want to set the difficulty close to 0 for faster mining.

{
  "config": {
    "chainId": 1907,
    "homesteadBlock": 0,
    "eip155Block": 0,
    "eip158Block": 0
  },
  "difficulty": "40",
  "gasLimit": "2100000",
  "alloc": {}
}

Create a new data directory for your first node, and launch the geth console:

mkdir node1
geth --datadir node1 init genesis.json
geth --datadir node1 console

Create your first account:

> personal.newAccount()

Simple commands in geth console:

> eth.coinbase // This will show your default address
> eth.accounts // Returns a list of addresses
> eth.getBalance(eth.coinbase)
> miner.start(1)
> miner.stop()
> personal.unlockAccount(eth.coinbase)
> eth.sendTransaction({from: eth.coinbase, to: eth.accounts[1], value: web3.toWei(3, "ether")}) // You need to mine this in order for transaction to be valid
> eth.hashrate // Check mining speed

Example contract simple.sol

pragma solidity ^0.4.13;

contract Simple {
  function arithmetics(uint _a, uint _b) returns (uint o_sum, uint o_product) {
    o_sum = _a + _b;
    o_product = _a * _b;
  }

  function multiply(uint _a, uint _b) returns (uint) {
    return _a * _b;
  }
}

Compile the contract:

# Compile into Simple.abi and Simple.bin
solc -o . --bin --abi simple.sol 

In the geth console, submit your contract:

> var simpleContract = eth.contract([{"constant":false,"inputs":[{"name":"_a","type":"uint256"},{"name":"_b","type":"uint256"}],"name":"multiply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_a","type":"uint256"},{"name":"_b","type":"uint256"}],"name":"arithmetics","outputs":[{"name":"o_sum","type":"uint256"},{"name":"o_product","type":"uint256"}],"payable":false,"stateMutability":"nonpayable","type":"function"}])

You may need to unlock your account before the next step:

> personal.unlockAccount(eth.coinbase)

Prefix the contents of Simple.bin with 0x, and assign to simple.data:

> var simple = simpleContract.new({from: eth.coinbase, data: "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", gas: 50000})

This contract would then need to be mined into the blockchain before its functions can be called.

> miner.start(1)
> miner.stop()
true
> simple.multiply
function()
> simple.multiply.call(4,5)
20
> simple.arithmetics.call(10,2)
[12, 20]

References

First steps with Ethereum Private Networks and Smart Contracts on Ubuntu 16.04