String to hex: xxd -p <<< "Blockchain Developer"
Hex to string: echo 426c6f636b636861696e20446576656c6f7065720a|xxd -r -p
String to Hex: xxd -p file.txt fileEncoded.txt
Hex to String: xxd -p -r fileEncoded.txt fileDecoded.txt

Image to Hex: xxd -p img.png img.txt
Hex to Image: xxd -p -r img.txt imgDecoded.png

    <!-- Generate Private Key -->
    openssl ecparam -name secp256k1 -genkey -noout

    <!-- Generate a random Private Key & Derive a Public Key -->
    openssl ecparam -name secp256k1 -genkey -noout | openssl ec -text -noout > Key

    <!-- Generate the hash, and save to a file 'address' -->
    cat pub | keccak-256sum -x -l | tr -d ' -' | tail -c 41 > address

    npm install -g ganache-cli
    sudo npm install -g ganache-cli truffle

    <!-- Run Ganache CLI -->
    ganache-cli

    <!-- Stop Ganache and modify your Ganache command line statement to include --mnemonic "string of words". -->
    ganache-cli --mnemonic 'trick core barely fold sample icon display hollow smoke task emotion pepper'

    <!-- Compile smart contracts -->
    truffle compile

    <!-- Deploy smart contract -->
    <!-- Make sure to configure your network settings. Modify truffle.js file (or truffle-config.js for windows), example below: -->
    module.exports = {
    // See <http://truffleframework.com/docs/advanced/configuration>
    // to customize your Truffle configuration!
    networks: {
        development: {
        host: "localhost",
        port: 8545,
        network_id: "*" // Match any network id
        }
    }
    };

    <!-- Run the following command to start the migrations scripts and deploy your smart contracts: -->
    truffle migrate

 npm install http-server -g

 http-server [path] [options]
<!-- [path] defaults to ./public if the folder exists, and ./ otherwise. -->

- https://ethstats.net/
- https://github.com/ethereum/wiki/wiki/Glossary

n ls // list all available node versions
nvm install v0.4.12 // install certain version
nvm use v0.4.12 // user certain version

<!-- start regtest -->
bitcoind -regtest -daemon

<!-- generate 101 blocks -->
bitcoin-cli -regtest generate 101

<!-- get balance -->
bitcoin-cli -regtest getbalance

// 固定长度为2的静态数组:
uint[2] fixedArray;
// 固定长度为5的string类型的静态数组:
string[5] stringArray;
// 动态数组，长度不固定，可以动态添加元素:
uint[] dynamicArray;

Person[] people;