gistfile1.rb

require 'rubygems'
require 'libxml'

xml = <<END
<?xml version="1.0" encoding="UTF-8"?>
<location lat="54.444" long="23.232" />
END

#create parser for the xml string
parser = LibXML::XML::Parser.string(xml)

#parse the xml and turn it into a Document
doc = parser.parse

#this is where you can start to manipulate the data within the
#Document :-)

#for example, let's get all the location nodes and double their lat
#attribute
nodes = doc.find('/location')

nodes.each do |node|
  lattitude = node["lat"]
  double_lattitude = (lattitude.to_f * 2).to_s
  node["lat"] = double_lattitude
end

#now we can see the fruits of our labours. LibXML also sports a
#save method which saves directly to a file see: 
#http://libxml.rubyforge.org/rdoc/index.html
doc.to_s(:indent => true, :encoding => LibXML::XML::Encoding::UTF_8)