The full procedure:
Open a terminal and clone the github repository
git clone https://github.com/bitcoin/bitcoin
then get the latest stable version, right now the command is:
git fetch
git checkout 0.11
then build bitcoin-core as ususal (install the required lib dependencies, ./autogen.sh, ./configure, make, make install)
The current development version is 11.99, you can build multiple version of bitcoin, for example a development version and a stable version to test beta features and to see if the private keys / blockchain / backups are easily loaded on the dev version, this is the json output of the getinfo
bitcoin-cli
command/function that lets you check the version numbers:
version: 11.9900
protocolversion: 7.0011
walletversion: 6.0000
this means we are running 0.11.99 (it means the future 0.12)
protocol version is 7.00.11
wallet version is 6
extra infos:
the current versions are also stored in JSON on the bitcoin blockchain: 91b37d9429a7e660a6b2c3352e39335e81884493dfbfbffa479b8068194e921d (transaction hash)
https://chain.so/tx/BTC/91b37d9429a7e660a6b2c3352e39335e81884493dfbfbffa479b8068194e921d see the message field on sochain or blockchain.info https://blockchain.info/tx/91b37d9429a7e660a6b2c3352e39335e81884493dfbfbffa479b8068194e921d