script using bx libbitcoin-explorer to create a transaction ready to send to the bitcoin network

transact.rb

#!/usr/bin/env ruby
require 'json'
require 'active_support/core_ext/hash/conversions'

# BX libbitcoin-explorer

SRC_ADDR=""
DEST_ADDR=""
CHANGE_ADDR=""

OUTPUTS = [
  [ DEST_ADDR,   10328414 ],
  [ CHANGE_ADDR,   328414 ],
]

def arraytypes(out)
  %w(transfers inputs outputs).each do |type|
    out.sub! "<#{type}>", "<#{type} type=\"array\">"
  end
end

def bx(cmd, *args, xml: false)
  cmd = cmd.to_s.tr '_', '-'
  cmdline = "bx #{cmd} "
  cmdline += "-f xml " if xml
  cmdline += args.join(' ')
  out = `#{cmdline}`.strip
  return out unless xml
  arraytypes out
  Hash.from_xml(out)
end

def fetch_input_transaction_id(addr)
  history = bx :fetch_history, addr, xml: true
  history.dig 'transfers', 0, 'received', 'hash'
end

def fetch_input(tx_id, addr)
  tx = bx :fetch_tx, tx_id, xml: true
  outputs = tx.dig 'transaction', 'outputs'

  i = 0
  outputs.each { |o| o['index'] = i; i += 1 }
  outputs.find { |o| o['address'] == addr }
end

def create_tx(addr, outputs)
  tx_id = fetch_input_transaction_id(addr)
  input = fetch_input(tx_id, addr)

  tx = tx_encode(input_def(tx_id, input), outputs)
  puts "Fee:", fee(input['value'], outputs)
  endorsement = sign_input(ec_private_key, input['script'], tx)

  set_script(endorsement, public_key(wif_private_key), tx)
end

def set_script(endorsement, pubkey, tx)
  bx :input_set, %("[ #{endorsement} ] [ #{pubkey} ]"), tx
end

def sign_input(key, script, tx)
  bx :input_sign, key, "'#{script}'", tx
end

def ec_private_key
  bx :wif_to_ec, wif_private_key
end

def wif_private_key
  ENV['PRIVKEY']
end

def public_key(key)
  bx :wif_to_public, key
end

def input_def(tx_id, input)
  "#{tx_id}:#{input['index']}"
end

def tx_encode(input, outputs)
  outputs = outputs.map { |o| ' -o ' + o.join(':') }.join
  bx :tx_encode, '-i', input, outputs
end

def fee(input, outputs)
  input.to_i - outputs.map { |o| o[1] }.reduce(:+)
end


puts create_tx(SRC_ADDR, OUTPUTS)