doc_files_at_command_line.rb

require 'nokogiri'

system 'unzip Alliance.docx'
doc = Nokogiri::XML(open('word/document.xml'))

# Using Label Tag
doc.xpath("//w:fldSimple[contains(@w:instr, 'label_tag')]").each do |link|
  command = link.attributes["instr"].value.match(/\#\{(.*)\}/)[1]
  replacement_string = eval(command)
  element.replace(Nokogiri::XML::Text.new(replacement_string, doc))
end