Module 5: Transactions and UTXO control

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Learning objectives

• Understand the UTXO model and inspect your spendable outputs
• Build and sign a raw transaction from scratch
• Broadcast a transaction to the regtest network
• Decode and analyze a transaction using Bitcoin Core tools

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What is the UTXO model?

• Each output is discrete and must be fully spent
• Change goes back to you as a new UTXO
• Wallets typically manage this automatically

bitcoin-cli -regtest listunspent

[
  {
    "txid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
    "vout": 0,
    "address": "bcrt1qw508d6qejxtdg4y5r3zarvary0c5xw7kygt080",
    "amount": 50.00000000,
    "confirmations": 101,
    "spendable": true,
    "solvable": true,
    "safe": true
  }
]

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Funding transactions manually

1. Choose an input UTXO (txid and vout)
2. Specify your outputs (recipient address + amount, and change)
3. Create, sign, and send the transaction

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Creating a raw transaction

bitcoin-cli -regtest createrawtransaction \
  '[{"txid":"abc123...","vout":0}]' \
  '{"bcrt1qrecipient...":0.5,"bcrt1qchangeaddress...":49.4999}'

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Signing the raw transaction

bitcoin-cli -regtest signrawtransactionwithwallet <raw_tx_hex>

• The signed hex
• A boolean complete: true if fully signed

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Broadcasting the transaction

bitcoin-cli -regtest sendrawtransaction <signed_tx_hex>

bitcoin-cli -regtest generatetoaddress 1 <miner_address>

bitcoin-cli -regtest gettransaction <txid>

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Decoding transactions

bitcoin-cli -regtest decoderawtransaction <tx_hex>

• vin (inputs): where the funds came from
• vout (outputs): destination addresses and values
• Script types (e.g. witness_v0_keyhash)

• Debugging transaction construction
• Verifying output order and structure
• Teaching UTXO mechanics

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Activity

1. Mine 101 blocks to have spendable BTC
2. Use the listunspent command to find UTXO
3. Create a raw transaction sending 0.5 BTC to another address
4. Sign it with your wallet
5. Broadcast and mine 1 block
6. Decode the transaction with decoderawtransaction