The command line from a Linux script
************************************




..
    Slide http://ui-tutorweb.clifford.shuttlethread.com/comp/crypto251.0/lec04000/sl04010
The Linux shell
===============

The bash shell accepts commands such as

* ls
* cd

Output can be redirected into other programs or into a file

* ls | sort
* ls > delete.me

Most commands are just programs. Commands may take command-line options.

* smileycoin-cli getinfo
* smileycoin-cli listunspent




..
    Slide http://ui-tutorweb.clifford.shuttlethread.com/comp/crypto251.0/lec04000/sl04020
Startup files
=============

Many programs use a startup file if it exists somewhere

* .smileycoin/smileycoin.conf

The Smileycoin/Bitcoin/Litecoin config files change the behaviour of the wallets

Example:

* walletnotify=/home/user/bin/readIncoming %s

specifies a command to be run every time an incoming transaction is observer

The script ``readIncoming`` must exist and be executable. It should assume that there is one argument, the transaction id. Commonly this is a ``shell script``, which is just a collection of shell commands.




..
    Slide http://ui-tutorweb.clifford.shuttlethread.com/comp/crypto251.0/lec04000/sl04030
Betzy
=====

`Betzyyy 
<https://steemit.com/blockchain/@gstefans/double-or-nothing-on-the-blockchain/>`_
is an example of a Linux script which is called to handle incoming transactions.

See


https://steemit.com/blockchain/@gstefans/double-or-nothing-on-the-blockchain

-- though ``BEtZyyYqDXqmRJJ45nnL15cuASfiXg9Yik`` is more commonly used as the recipient address

Handout
-------

Check the script ``ATMDoubleOrNothing`` to see exactly how this works, based on just adding the command

::

  walletnotify=/home/gstefans/atm/ATMDoubleOrNothing %s

to ``smileycoin.conf``. Note that the script is available on `github <https://github.com/gstefans/ATM>`_.

Note also that there is a difference between the notification commands

::

  walletnotify=/home/.../script1 %s
  blocknotify=/home/.../script1 %s
  



..
    Slide http://ui-tutorweb.clifford.shuttlethread.com/comp/crypto251.0/lec04000/sl04040
The command script
==================

Upon startup, a typical ``readIncoming script`` will call the wallet to inspect the incoming transaction:


* txId=$1
* smileycoin-cli  gettransaction $txId
* tx=`smileycoin-cli  getrawtransaction $txId`
* stuff=`smileycoin-cli  decoderawtransaction $tx`

and then inspect the elements of ``stuff`` to extract whatever data is needed.