Now that all the setup is complete, we can move onto deploying and interacting with contracts. While in the Foundry project directory, you can deploy your contract using the forge create command. Here’s how to deploy a Counter.sol contract: 
forge create --rpc-url $RPC_URL \
--private-key $PRIVATE_KEY \
src/Counter.sol:Counter
The command breakdown:
  • forge create: The command to deploy a contract
  • --rpc-url: Your network’s RPC URL
  • --private-key: Your wallet’s private key (never share this!)
  • src/Counter.sol:Counter: The path to your contract file and the contract name after the colon

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Importance of Dry Runs

This will generate a build version of the contract. This is always good to run before actually deploying onto blockchain in order to see what if command has bugs but more importantly save money. If you deployment, you will still pay gas fees.

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Real Run

To put the transaction on Testnet, we will need to add the --broadcast flag at the end of the function. 
forge create --rpc-url $RPC_URL \
--private-key $PRIVATE_KEY \
src/Counter.sol:Counter --broadcast
The output will resemble this 
Deployer: 0xbb6545183E3cF15Fc8caCcCef0d40976579fbD35
Deployed to: 0x0fDd28683A2D282c963f42b89408dcA529F6DB78
Transaction hash: 0xe004f68c94e0a6db38a56e609ddec49e75f5a8fcaa0a4cabd91035c6b27501b9
  • Deployer -> Your public address
  • Deployed to -> Deployed contract address
  • Transaction hash -> Transaction that we just signed above ^
Put this into Sepolia Ether Scan to analyze the transaction and contract hash.

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Interacting with the Smart Contract

It doesn’t cost money to view the state of the blockchain. Notice that viewing the blockchain we use call. 
cast call 0x0fDd28683A2D282c963f42b89408dcA529F6DB78 "number()" \
--rpc-url $RPC_URL

cast --to-dec <HEXA-VALUE>
Changing the state on the blockchain requires paying gas. Viewing does not, hence why we are not signing with our private key
cast send 0x0fDd28683A2D282c963f42b89408dcA529F6DB78 "setNumber(uint256)" 42 \
--rpc-url $RPC_URL \
--private-key $PRIVATE_KEY