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Joseph Goulden edited this page Aug 11, 2015 · 63 revisions

Account types and transactions

There are two types of accounts in Ethereum state:

  • Normal or externally controlled accounts and
  • contracts, i.e., snippets of code, think a class.

Both types of accounts have an ether balance.

Transactions can be fired from both types of accounts, though contracts only fire transactions in response to other transactions that they have received. Therefore, all action on the ethereum block chain is set in motion by transactions fired from externally-controlled accounts.

The simplest transactions are ether transfer transactions. But before we go into that you should read up on accounts and perhaps on mining.

Ether transfer

Assuming the account you are using as sender has sufficient funds, sending ether couldn't be easier. Which is also why you should probably be careful with this! You have been warned.

eth.sendTransaction({from: '0x036a03fc47084741f83938296a1c8ef67f6e34fa', to: '0xa8ade7feab1ece71446bed25fa0cf6745c19c3d5', value: web3.toWei(1, "ether")})

Note the unit conversion in the value field. Transaction values are expressed in weis, the most granular units of value. If you want to use some other unit (like ether in the example above), use the function web3.toWei for conversion.

Also, be advised that the amount debited from the source account will be slightly larger than that credited to the target account, which is what has been specified. The difference is a small transaction fee, discussed in more detail later.

Contracts can receive transfers just like externally controlled accounts, but they can also receive more complicated transactions that actually run (parts of) their code and update their state. In order to understand those transactions, a rudimentary understanding of contracts is required.

Writing a contract

Contracts live on the blockchain in an Ethereum-specific binary format (Ethereum Virtual Machine (=EVM) bytecode). However, contracts are typically written in some high level language such as solidity and then compiled into byte code to be uploaded on the blockchain.

Note that other languages also exist, notably serpent and LLL. Legacy Mutan (an early c-like language) is no longer officially maintained.

Language Resources

Solidity

Docs and tutorials

Examples

Compilers

Serpent

Contract/Dapp development environments and frameworks

Compiling a contract

Contracts live on the blockchain in an Ethereum-specific binary format (Ethereum Virtual Machine (=EVM) bytecode). However, contracts are typically written in some high level language such as solidity and then compiled into byte code to be uploaded on the blockchain.

For the frontier release, geth supports solidity compilation through system call to solc, the command line solidity compiler by Christian R. and Lefteris K. You can try Solidity realtime compiler (by Christian R) or Cosmo or Mix.

If you start up your geth node, you can check if the solidity compiler is available. This is what happens, if it is not:

> eth.compile.solidity("")
eth_compileSolidity method not available: solc (solidity compiler) not found
    at InvalidResponse (<anonymous>:-57465:-25)
    at send (<anonymous>:-115373:-25)
    at solidity (<anonymous>:-104109:-25)
    at <anonymous>:1:1

After you found a way to install solc, you make sure it's in the path. If eth.getCompilers() still does not find it (returns an empty array), you can set a custom path to the solc executable on the command line using th solc flag.

geth --datadir ~/frontier/00 --solc /usr/local/bin/solc --natspec

You can also set this option at runtime via the console:

> admin.setSolc("/usr/local/bin/solc")
solc v0.9.32
Solidity Compiler: /usr/local/bin/solc
Christian <c@ethdev.com> and Lefteris <lefteris@ethdev.com> (c) 2014-2015
true

Let us take this simple contract source:

> source = "contract test { function multiply(uint a) returns(uint d) { return a * 7; } }"

This contract offers a unary method: called with a positive integer a, it returns a * 7.

You are ready to compile solidity code in the geth JS console using eth.compile.solidity:

> contract = eth.compile.solidity(source).test
{
  code: '605280600c6000396000f3006000357c010000000000000000000000000000000000000000000000000000000090048063c6888fa114602e57005b60376004356041565b8060005260206000f35b6000600782029050604d565b91905056',
  info: {
    language: 'Solidity',
    languageVersion: '0',
    compilerVersion: '0.9.13',
    abiDefinition: [{
      constant: false,
      inputs: [{
        name: 'a',
        type: 'uint256'
      } ],
      name: 'multiply',
      outputs: [{
        name: 'd',
        type: 'uint256'
      } ],
      type: 'function'
    } ],
    userDoc: {
      methods: {
      }
    },
    developerDoc: {
      methods: {
      }
    },
    source: 'contract test { function multiply(uint a) returns(uint d) { return a * 7; } }'
  }
}

The compiler is also available via RPC and therefore via web3.js to any in-browser Ðapp connecting to geth via RPC/IPC.

The following example shows how you interface geth via JSON-RPC to use the compiler.

./geth --datadir ~/eth/ --loglevel 6 --logtostderr=true --rpc --rpcport 8100 --rpccorsdomain '*' --mine console  2>> ~/eth/eth.log
curl -X POST --data '{"jsonrpc":"2.0","method":"eth_compileSolidity","params":["contract test { function multiply(uint a) returns(uint d) { return a * 7; } }"],"id":1}' http://127.0.0.1:8100

The compiler output for one source will give you contract objects each representing a single contract. The actual return value of eth.compile.solidity is a map of contract name -- contract object pairs. Since our contract's name is test, eth.compile.solidity(source).test will give you the contract object for the test contract containing the following fields:

The immediate structuring of the compiler output (into code and info) reflects the two very different paths of deployment. The compiled EVM code is sent off to the blockchain with a contract creation transaction while the rest (info) will ideally live on the decentralised cloud as publicly verifiable metadata complementing the code on the blockchain.

If your source contains multiple contracts, the output will contain an entry for each contact, the corresponding contract info object can be retrieved with the name of the contract as attribute name. You can try this by inspecting the most current GlobalRegistrar code:

contracts = eth.compile.solidity(globalRegistrarSrc)

Creating and deploying a contract

Now that you got both an unlocked account as well as some funds, you can create a contract on the blockchain by sending a transaction to the empty address with the evm code as data. Simple, eh?

primaryAddress = eth.accounts[0]
MyContract = eth.contract(abi);
contact = MyContract.new(arg1, arg2, ...,{from: primaryAddress, data: evmCode})

All binary data is serialised in hexadecimal form. Hex strings always have a hex prefix 0x.

Note that arg1, arg2, ... are the arguments for the contract constructor, in case it accepts any.

Also note that this step requires you to pay for execution. Your balance on the account (that you put as sender in the from field) will be reduced according to the gas rules of the VM once your transaction makes it into a block. More on that later. After some time, your transaction should appear included in a block confirming that the state it brought about is a consensus. Your contract now lives on the blockchain.

The asynchronous way of doing the same looks like this:

MyContract.new([arg1, arg2, ...,]{from: primaryAccount, data: evmCode}, function(err, contract) {
  if (!err && contract.address)
    console.log(contract.address); 
});

Gas and transaction costs

So how did you pay for all this? Under the hood, the transaction specified a gas limit and a gasprice, both of which could have been specified directly in the transaction object.

Gas limit is there to protect you from buggy code running until your funds are depleted. The product of gasPrice and gas represents the maximum amount of Wei that you are willing to pay for executing the transaction. What you specify as gasPrice is used by miners to rank transactions for inclusion in the blockchain. It is the price in Wei of one unit of gas, in which VM operations are priced.

The gas expenditure incurred by running your contract will be bought by the ether you have in your account at a price you specified in the transaction with gasPrice. If you do not have the ether to cover all the gas requirements to complete running your code, the processing aborts and all intermediate state changes roll back to the pre-transaction snapshot. The gas used up to the point where execution stopped were used after all, so the ether balance of your account will be reduced. These parameters can be adjusted on the transaction object fields gas and gasPrice. The value field is used the same as in ether transfer transactions between normal accounts. In other words transferring funds is available between any two accounts, either normal (i.e. externally controlled) or contract. If your contract runs out of funds, you should see an insufficient funds error.

For testing and playing with contracts you can use the test network or set up a private node (or cluster) potentially isolated from all the other nodes. If you then mine, you can make sure that your transaction will be included in the next block. You can see the pending transactions with:

eth.getBlock("pending", true).transactions

You can retrieve blocks by number (height) or by their hash:

genesis = eth.getBlock(0)
eth.getBlock(genesis.hash).hash == genesis.hash
true

Use eth.blockNumber to get the current blockchain height and the "latest" magic parameter to access the current head (newest block).

currentHeight = eth.blockNumber()
eth.getBlock("latest").hash == eth.getBlock(eth.blockNumber).hash
true

Contract info (metadata)

In the previous sections we explained how you create a contract on the blockchain. Now we deal with the rest of the compiler output, the contract metadata or contract info. The idea is that

  • contract info is uploaded somewhere identifiable by a url which is publicly accessible
  • anyone can find out what the url is only knowing the contracts address

These requirements are achieved very simply by using a 2 step blockchain registry. The first step registers the contract code (hash) with a content hash in a contract called HashReg. The second step registers a url with the content hash in the UrlHint contract. These simple registry contracts will be part of the frontier proposition.

By using this scheme, it is sufficient to know a contract's address to look up the url and fetch the actual contract metadata info bundle. Read on to learn why this is good.

So if you are a conscientious contract creator, the steps are the following:

  1. Deploy the contract itself to the blockchain
  2. Get the contract info json file.
  3. Deploy contract info json file to any url of your choice
  4. Register codehash ->content hash -> url

The JS API makes this process very easy by providing helpers. Call admin.register to extract info from the contract, write out its json serialisation in the given file, calculates the content hash of the file and finally registers this content hash to the contract's code hash. Once you deployed that file to any url, you can use admin.registerUrl to register the url with your content hash on the blockchain as well. (Note that in case a fixed content addressed model is used as document store, the url-hint is no longer necessary.)

source = "contract test { function multiply(uint a) returns(uint d) { return a * 7; } }"
// compile with solc
contract = eth.compile.solidity(source).test
// create contract object
var MyContract = eth.contract(contract.info.abiDefinition)
// extracts info from contract, save the json serialisation in the given file, 
contenthash = admin.saveInfo(contract.info, "~/dapps/shared/contracts/test/info.json")
// send off the contract to the blockchain
MyContract.new({from: primaryAccount, data: contract.code}, function(error, contract){
  if(!error && contract.address) {
    // calculates the content hash and registers it with the code hash in `HashReg`
    // it uses address to send the transaction. 
    // returns the content hash that we use to register a url
    admin.register(primaryAccount, contract.address, contenthash)
    // here you deploy ~/dapps/shared/contracts/test/info.json to a url
    admin.registerUrl(primaryAccount, hash, url)
  }
});

Interacting with contracts

eth.contract can be used to define a contract class that will comply with the contract interface as described in its ABI definition.

var Multiply7 = eth.contract(contract.info.abiDefinition);
var myMultiply7 = Multiply7.at(address);

Now all the function calls specified in the abi are made available on the contract instance. You can just call those methods on the contract instance and chain sendTransaction({from: address}) or call() to it. The difference between the two is that call performs a "dry run" locally, on your computer, while sendTransaction would actually submit your transaction for inclusion in the block chain and the results of its execution will eventually become part of the global consensus. In other words, use call, if you are interested only in the return value and use sendTransaction if you only care about "side effects" on the state of the contract.

In the example above, there are no side effects, therefore sendTransaction only burns gas and increases the entropy of the universe. All "useful" functionality is exposed by call:

myMultiply7.multiply.call(6)
42

Now suppose this contract is not yours, and you would like documentation or look at the source code. This is made possible by making available the contract info bundle and register it in the blockchain. The admin API provides convenience methods to fetch this bundle for any contract that chose to register. To see how it works, read about Contract Metadata or read the contract info deployment section of this document.

// get the contract info for contract address to do manual verification
var info = admin.getContractInfo(address) // lookup, fetch, decode
var source = info.source;
var abiDef = info.abiDefinition

NatSpec

This section will further elaborate what you can do with contracts and transactions building on a protocol NatSpec. Solidity implements smart comments doxigen style which then can be used to generate various facades meta documents of the code. One such use case is to generate custom messages for transaction confirmation that clients can prompt users with.

So we now extend the multiply7 contract with a smart comment specifying a custom confirmation message (notice).

contract test {
   /// @notice Will multiply `a` by 7.
   function multiply(uint a) returns(uint d) {
       return a * 7;
   }
}

The comment has expressions in between backticks which are to be evaluated at the time the transaction confirmation message is presented to the user. The variables that refer to parameters of method calls then are instantiated in accordance with the actual transaction data sent by the user (or the user's dapp). NatSpec support for confirmation notices is fully implemented in geth. NatSpec relies on both the abi definition as well as the userDoc component to generate the proper confirmations. Therefore in order to access that, the contract needs to have registered its contract info as described above.

Let us see a full example. As a very conscientious smart contract dev, you first create your contract and deploy according to the recommended steps above:

source = "contract test {
   /// @notice Will multiply `a` by 7.
   function multiply(uint a) returns(uint d) {
       return a * 7;
   }
}"
contract = eth.compile.solidity(source).test
MyContract = eth.contract(contract.info.abiDefinition)
contenthash = admin.saveInfo(contract.info, "~/dapps/shared/contracts/test/info.json")
MyContract.new({from: primary, data: contract.code}, function(error, contract){
  if(!error && contract.address) {
    admin.register(primary, contract.address, contenthash)
    // put it up on your favourite oldworld site:
    admin.registerUrl(contentHash, "http://dapphub.com/test/info.json")
  }
});

Note that if we use content addressed storage system like swarm the second step is unnecessary, since the contenthash is (deterministically translates to) the unique address of the content itself.

For the purposes of a painless example just simply use the file url scheme (not exactly the cloud, but will show you how it works) without needing to deploy.

admin.registerUrl(contentHash, "file:///home/nirname/dapps/shared/contracts/test/info.json")

Now you are done as a dev, so swap seats as it were and pretend that you are a user who is sending a transaction to the infamous multiply7 contract.

You need to start the client with the --natspec flag to enable smart confirmations and contractInfo fetching. You can also set it on the console with admin.startNatSpec() and admin.stopNatSpec().

geth --natspec --unlock primary console 2>> /tmp/eth.log

Now at the console type:

// obtain the abi definition for your contract
var info = admin.getContractInfo(address)
var abiDef = info.abiDefinition
// instantiate a contract for transactions
var Multiply7 = eth.contract(abiDef);
var myMultiply7 = Multiply7.at(address);

And now try to send an actual transaction:

> myMultiply7.multiply.sendTransaction(6)
NatSpec: Will multiply 6 by 7. 
Confirm? [y/n] y
>

When this transaction gets included in a block, somewhere on a lucky miner's computer, 6 will get multiplied by 7, with the result ignored. Mission accomplished.

If the transaction is not picked up, we can see it with:

eth.pendingTransactions

This accumulates all the transactions sent, even the ones that were rejected and are not included in the current mined block (trans state). These latter can be shown by:

eth.getBlock("pending", true).transactions()

if you identify the index of your rejected transaction, you can resend it with modified gas limit and gas price (both optional parameters):

tx = eth.pendingTransactions[1]
eth.resend(tx, newGasPrice, newGasLimit)

Testing contracts and transactions

Often you need to resort to a low level strategy of testing and debugging contracts and transactions. This section introduces some debug tools and practices you can use. In order to test contracts and transactions without real-word consequences, you best test it on a private blockchain. This can be achieved with configuring an alternative network id (select a unique integer) and/or disable peers. It is recommended practice that for testing you use an alternative data directory and ports so that you never even accidentally clash with your live running node (assuming that runs using the defaults. Starting your geth with in VM debug mode with profiling and highest logging verbosity level is recommended:

geth --datadir ~/dapps/testing/00/ --port 30310 --rpcport 8110 --networkid 4567890 --nodiscover --maxpeers 0 --vmdebug --verbosity 6 --pprof --pprofport 6110 console 2>> ~/dapp/testint/00/00.log

Before you can submit any transactions, you need mine some ether on your private chain and for that you need an account. See the sections on Mining and Accounts

// create account. will prompt for password
personal.newAccount("mypassword");
// name your primary account, will often use it
primary = eth.accounts[0];
// check your balance (denominated in ether)
balance = web3.fromWei(eth.getBalance(primary), "ether");
// assume an existing unlocked primary account
primary = eth.accounts[0];

// mine 10 blocks to generate ether 

// starting miner
miner.start(8);
// sleep for 10 blocks.
admin.sleepBlocks(10);
// then stop mining (just not to burn heat in vain)
miner.stop()  ;
balance = web3.fromWei(eth.getBalance(primary), "ether");

After you create transactions, you can force process them with the following lines:

miner.start(1);
admin.sleepBlocks(1);
miner.stop()  ;

you can check your pending transactions with

// shows transaction pool
txpool.status
// number of pending txs
eth.getBlockTransactionCount("pending");
// print all pending txs
eth.getBlock("pending", true).transactions

If you submitted contract creation transaction, you can check if the desired code actually got inserted in the current blockchain:

txhash = eth.sendTansaction({from:primary, data: code})
//... mining
contractaddress = eth.getTxReceipt(txhash);
eth.getCode(contractaddress)

Registrar services

The frontier chain comes with some very basic baselayer services, most of all the registrar. The registrar is composed of 3 components.

  • GlobalRegistrar to associate names (strings) to accounts (addresses).
  • HashReg to associate hashes to hashes (map any object to a 'content' hash.
  • UrlHint to associate content hashes to a hint for the location of the content. This is needed only if content storage is not content addressed, otherwise content hash is already the content address. If it is used, content fetched from the url should hash to content hash. In order to check authenticity of content one can check if this verifies.

Create and deploy GlobalRegistrar, HashReg and UrlHint

If the registrar contracts are not hardcoded in the blockchain (they are not at the time of writing), the registrars need to be deployed at least once on every chain.

If you are on the main live chain, the address of the main global registrar is hardcoded in the latest clients and therefore you do not need to do anything. If you want to change this or you are on a private chain you need to deploy these contracts at least once:

primary = eth.accounts[0];

globalRegistrarAddr = admin.setGlobalRegistrar("", primary);
hashRegAddr = admin.setHashReg("", primary);
urlHintAddr = admin.setUrlHint("", primary);

You need to mine or wait till the txs are all picked up. Initialise the registrar on the new address and check if the other registrars' names resolve to the correct addresses:

registrar = GlobalRegistrar.at(globalRegistrarAddr);
primary == registrar.owner("HashReg");
primary == registrar.owner("UrlHint");
hashRegAddr == registrar.addr("HashReg");
urlHintAddr registrar.addr("UrlHint");

and the following ones return correct code:

eth.getCode(registrar.address);
eth.getCode(registrar.addr("HashReg"));
eth.getCode(registrar.addr("UrlHint"));

From the second time onwards on the same chain as well as on other nodes, you simply seed with the GlobalRegistrars address, the rest is handled through it.

primary = eth.accounts[0];
globalRegistrarAddr = "0x225178b4829bbe7c9f8a6d2e3d9d87b66ed57d4f"

// set the global registrar address
admin.setGlobalRegistrar(globalRegistrarAddr)
// set HashReg address via globalRegistrar
hashRegAddr = admin.setHashReg()
// set UrlHint address via globalRegistrar
urlHintAddr = admin.setUrlHint()

// (re)sets the registrar variable to a GlobalRegistrar contract instance 
registrar = GlobalRegistrar.at(globalRegistrarAddr);

If this is successful, you should be able to check with the following commands if the registrar returns addresses:

registrar.owner("HashReg");
registrar.owner("UrlHint");
registrar.addr("HashReg");
registrar.addr("UrlHint");

and the following ones return correct code:

eth.getCode(registrar.address);
eth.getCode(registrar.addr("HashReg"));
eth.getCode(registrar.addr("UrlHint"));

Using the registrar services

Can provide useful interfaces between contracts and dapps.

Global registrar

To reserve a name register an account address with it, you need the following:

registrar.reserve.sendTransaction(name, {from:primary})
registrar.setAddress.sendTransaction (name, address, true, {from: primary})

You need to wait for the transactions to be picked up (or force mine them if you are on a private chain). To check you query the registrar:

registrar.owner(name)
registrar.addr(name)

HashReg and UrlHint

HashReg and UrlHint can be used with the following abis:

hashRegAbi = '[{"constant":false,"inputs":[],"name":"setowner","outputs":[],"type":"function"},{"constant":false,"inputs":[{"name":"_key","type":"uint256"},{"name":"_content","type":"uint256"}],"name":"register","outputs":[],"type":"function"}]'
urlHintAbi = '[{"constant":false,"inputs":[{"name":"_hash","type":"uint256"},{"name":"idx","type":"uint8"},{"name":"_url","type":"uint256"}],"name":"register","outputs":[],"type":"function"}]'

setting up the contract instances:

hashReg = eth.contract(hashRegAbi).at(registrar.addr("HashReg")));
urlHint = eth.contract(UrlHintAbi).at(registrar.addr("UrlHint")));

Associate a content hash to a key hash:

hashReg.register.sendTransaction(keyhash, contenthash, {from:primary})

Associate a url to a content hash:

urlHint.register.sendTransaction(contenthash, url, {from:primary})

To check resolution:

contenthash = hashReg._hash(keyhash);
url = urlHint._url(contenthash);

Example script

The example script below demonstrates most features discussed in this tutorial. You can run it with the JSRE as geth js script.js 2>>geth.log . If you want to run this test on a local private chain, then start geth with:

geth --maxpeers 0 --networkid 123456 --nodiscover --unlock primary js script.js 2>> geth.log

Note that networkid can be any arbitrary non-negative integer, 0 is always the live net.

personal.newAccount("")

primary = eth.accounts[0];
balance = web3.fromWei(eth.getBalance(primary), "ether");
personal.unlockAccount(primary, "00");
// miner.setEtherbase(primary)

miner.start(8); admin.sleepBlocks(10); miner.stop()  ;

// 0xc6d9d2cd449a754c494264e1809c50e34d64562b
primary = eth.accounts[0];
balance = web3.fromWei(eth.getBalance(primary), "ether");

globalRegistrarTxHash = admin.setGlobalRegistrar("0x0");
//'0x0'
globalRegistrarTxHash = admin.setGlobalRegistrar("", primary);
//'0xa69690d2b1a1dcda78bc7645732bb6eefcd6b188eaa37abc47a0ab0bd87a02e8'
miner.start(1); admin.sleepBlocks(1); miner.stop();
//true
globalRegistrarAddr = eth.getTransactionReceipt(globalRegistrarTxHash).contractAddress;
//'0x3d255836f5f8c9976ec861b1065f953b96908b07'
eth.getCode(globalRegistrarAddr);
//...
admin.setGlobalRegistrar(globalRegistrarAddr);
registrar = GlobalRegistrar.at(globalRegistrarAddr);

hashRegTxHash = admin.setHashReg("0x0");
hashRegTxHash = admin.setHashReg("", primary);
txpool.status
miner.start(1); admin.sleepBlocks(1); miner.stop();
hashRegAddr = eth.getTransactionReceipt(hashRegTxHash).contractAddress;
eth.getCode(hashRegAddr);

registrar.reserve.sendTransaction("HashReg", {from:primary});
registrar.setAddress.sendTransaction("HashReg",hashRegAddr,true, {from:primary});
miner.start(1); admin.sleepBlocks(1); miner.stop();
registrar.owner("HashReg");
registrar.addr("HashReg");

urlHintTxHash = admin.setUrlHint("", primary);
miner.start(1); admin.sleepBlocks(1); miner.stop();
urlHintAddr = eth.getTransactionReceipt(urlHintTxHash).contractAddress;
eth.getCode(urlHintAddr);

registrar.reserve.sendTransaction("UrlHint", {from:primary});
registrar.setAddress.sendTransaction("UrlHint",urlHintAddr,true, {from:primary});
miner.start(1); admin.sleepBlocks(1); miner.stop();
registrar.owner("UrlHint");
registrar.addr("UrlHint");

globalRegistrarAddr = "0xfd719187089030b33a1463609b7dfea0e5de25f0"
admin.setGlobalRegistrar(globalRegistrarAddr);
registrar = GlobalRegistrar.at(globalRegistrarAddr);
admin.setHashReg("");
admin.setUrlHint("");

///// ///////////////////////////////

admin.stopNatSpec();
primary = eth.accounts[0];
personal.unlockAccount(primary, "00")

globalRegistrarAddr = "0xfd719187089030b33a1463609b7dfea0e5de25f0";
admin.setGlobalRegistrar(globalRegistrarAddr);
registrar = GlobalRegistrar.at(globalRegistrarAddr);
admin.setHashReg("0x0");
admin.setHashReg("");
admin.setUrlHint("0x0");
admin.setUrlHint("");


registrar.owner("HashReg");
registrar.owner("UrlHint");
registrar.addr("HashReg")
registrar.addr("UrlHint");


/////////////////////////////////////
eth.getBlockTransactionCount("pending");
miner.start(1); admin.sleepBlocks(1); miner.stop();

source = "contract test {\n" +
"   /// @notice will multiply `a` by 7.\n" +
"   function multiply(uint a) returns(uint d) {\n" +
"      return a * 7;\n" +
"   }\n" +
"} ";
contract = eth.compile.solidity(source).test;
txhash = eth.sendTransaction({from: primary, data: contract.code});

eth.getBlock("pending", true).transactions;

miner.start(1); admin.sleepBlocks(1); miner.stop();
contractaddress = eth.getTransactionReceipt(txhash).contractAddress;
eth.getCode(contractaddress);

multiply7 = eth.contract(contract.info.abiDefinition).at(contractaddress);
fortytwo = multiply7.multiply.call(6);

/////////////////////////////////

// register a name for the contract
registrar.reserve.sendTransaction(primary,  {from: primary});
registrar.setAddress.sendTransaction("multiply7", contractaddress, true, {from: primary});
////////////////////////

admin.stopNatSpec();
filename = "/info.json";
contenthash = admin.saveInfo(contract.info, "/tmp" + filename);
admin.register(primary, contractaddress, contenthash);
eth.getBlock("pending", true).transactions;
miner.start(1); admin.sleepBlocks(1); miner.stop();

admin.registerUrl(primary, contenthash, "file://" + filename);
eth.getBlock("pending", true).transactions;
miner.start(1); admin.sleepBlocks(1); miner.stop();

////////////////////

// retrieve contract address using global registrar entry with 'multply7'
contractaddress = registrar.addr("multiply7);
// retrieve the info using the url 
info = admin.getContractInfo(contractaddress);
multiply7 = eth.contract(info.abiDefinition).at(contractaddress);
// try Natspec
admin.startNatSpec();
fortytwo = multiply7.multiply.sendTransaction(6, { from: primary });

0x676f

You also need to add git to PATH

Main Ethereum Wiki

Frontier Release

Install and build

Installing Ethereum

Developers' Guide

Usage

Managing Accounts

Mining

Contracts and transactions

Contract Tutorial

Interface Documentation

Command Line Options

JavaScript Console

Management API

JSON-RPC server

Issues

Troubleshooting

FAQ

Reporting issues

Community and support

Legacy

Legacy pages

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