nokogiri add_chlid and remove child to xml

nokogiri.rb

#!/usr/bin/ruby

require 'nokogiri'

@file = File.open("/path/to/test.xml")
@xml = Nokogiri::XML(@file)
@file.close

@xml.at("hoge").children.remove
puts "# remove hoge children"
puts @xml

@fuga = Nokogiri::XML::Node.new "fuga", @xml
@fuga.content = "new content"
@xml.at("hoge").add_child(@fuga)

puts "# add_child at hoge"
puts @xml

result

# remove hoge children
<?xml version="1.0"?>
<root>
  <hoge/>
  <foo>
    <piyo>1</piyo>
  </foo>
</root>
# add_child at hoge
<?xml version="1.0"?>
<root>
  <hoge><fuga>new content</fuga></hoge>
  <foo>
    <piyo>1</piyo>
  </foo>
</root>

test.xml

<root>
  <hoge>
    <fuga>1</fuga>
    <fuga>2</fuga>
    <fuga>3</fuga>
  </hoge>
  <foo>
    <piyo>1</piyo>
  </foo>
</root>