# Example mock-tx

We can download a transaction from the network and execute it locally. To download a transaction, use [ckb-cli](https://github.com/nervosnetwork/ckb-cli):

```sh
$ ckb-cli --url https://mainnet.ckbapp.dev/rpc mock-tx dump --tx-hash 0x5f0a4162622daa0e50b2cf8f49bc6ece22d1458d96fc12a094d6f074d6adbb55 --output-file mock_tx.json
```

You can execute the lock script or type script in the transaction:

```sh
$ ckb-debugger --tx-file mock_tx.json --cell-index 0 --cell-type input --script-group-type lock

Run result: 0
Total cycles consumed: 1697297(1.6M)
Transfer cycles: 12680(12.4K), running cycles: 1684617(1.6M)
```

The option `--bin` gives ckb-debugger a chance to "replace" the script, We try to replace the running code in the transaction above with a new version of the lock.

```c
// always_failure.c
int main() {
    return 1;
}
```

```sh
$ ckb-debugger --tx-file mock_tx.json --cell-index 0 --cell-type input --script-group-type lock --bin always_failure

Run result: 1
Total cycles consumed: 1706(1.7K)
Transfer cycles: 764, running cycles: 942
```