bitcoind -daemon           # mainnet, -daemon will cause it to fork into the background
bitcoind -daemon -testnet  # testnet

bitcoin-cli getinfo           # mainnet, uses port  8332 for RPC-JSON
bitcoin-cli -testnet getinfo  # testnet, uses port 18332 for RPC-JSON

bitcoin-cli -testnet getinfo  ## sends command to port 18332
bitcoin-cli -regtest getinfo  ## also sends command to port 18332