Modify a `pom.xml` file in place so that when using `mvn package` it generates an executable jar file.

pom_editor.rb

#!/usr/bin/env ruby
require 'nokogiri'

if ARGV.length == 0
  puts "\nUSAGE:\n\tpom_editor.rb path/to/pom.xml\n\n"
end

filename = ARGV[0]
@doc = Nokogiri::XML.parse(File.read(filename))

group_id = @doc.at_css("groupId").text

jar_config = [
  '  <configuration>',
  '            <archive>',
  '              <manifest>',
  '                <addClasspath>true</addClasspath>',
  "                <mainClass>#{group_id}.App</mainClass>",
  '              </manifest>',
  '            </archive>',
  "          </configuration>\n        "].join("\n")

@doc.search('plugins plugin').each do |plugin|
  if plugin.at_css('artifactId').text == 'maven-jar-plugin'
    plugin.add_child(jar_config)
  end
end

File.rename(filename, filename + '.bak')
File.write(filename, @doc.to_xml)