Solidity tutorial - Global namespace

The global namespace is a set of implicitly declared variables and functions that you can reference and use in your contract code directly.

Global variable	Member	Description
Block	Blockhash(unit blocknumber)	Hash of given block
	Coinbase	Block’s miner’s address
	gaslimit	Block’s gas limit
	number	Block’s number
	timestamp	Block’s timestamp as UNIX epoch
msg	data	Full calldata body
	sender	Message sender (who is performing the current call)
	gas	Remaining gas
	value	Amount of Ether sent with the message, in Wei
tx	gasprice	Transaction gas price
	origin	Transaction sender (who originated the full call chain)

Global namespace for exception

require(bool condition): This is used to validate function
input.
assert(bool condition): This is used to validate contract
state or function state.

revert() : the execution and revert the contract state explicitly

selfdestruct (Ether recipient address): remove the current contract instance from the blockchain. This will uninstall the current instance from the blockchain and move the Ether present at the associated account to the specified recipient address

Global namespace for cryptographic hash functions

sha256()(from the SHA-2 family)

keccak256() (from the SHA-3family)