ruby – 如何使用nokogiri方法.xpath和.at_xpath

require 'rubygems'
require 'mechanize'

post_agent = WWW::Mechanize.new
post_page = post_agent.get('http://www.vbulletin.org/forum/showthread.php?t=230708')

puts "nabsolute path with tbody gives nil"
puts  post_page.parser.xpath('/html/body/div/div/div/div/div/table/tbody/tr/td/div[2]').xpath('text()').to_s.strip.inspect

puts "n.at_xpath gives an empty string"
puts post_page.parser.at_xpath("//div[@id='posts']/div/table/tr/td/div[2]").at_xpath('text()').to_s.strip.inspect

puts "ntwo lines solution with .at_xpath gives an empty string"
rows =   post_page.parser.xpath("//div[@id='posts']/div/table/tr/td/div[2]")
puts rows[0].at_xpath('text()').to_s.strip.inspect


puts
puts "two lines working code"
rows =   post_page.parser.xpath("//div[@id='posts']/div/table/tr/td/div[2]")
puts rows[0].xpath('text()').to_s.strip

puts "none line working code"
puts post_page.parser.xpath("//div[@id='posts']/div/table/tr/td/div[2]")[0].xpath('text()').to_s.strip

puts "nanother one line code"
puts post_page.parser.at_xpath("//div[@id='posts']/div/table/tr/td/div[2]").xpath('text()').to_s.strip

puts "none line code with full path"
puts post_page.parser.xpath("/html/body/div/div/div/div/div/table/tr/td/div[2]")[0].xpath('text()').to_s.strip

>在xpath中使用//或/更好吗？ @AnthonyWJones说’使用没有前缀的//’并不是一个好主意
>我必须从任何工作的xpath中删除tbody,否则我得到’nil’结果.如何从xpath中删除元素以使其工作？
>如果不使用完整的xpath,我必须使用.xpath两次提取数据吗？
>为什么我不能让.at_xpath工作来提取数据？它的效果很好here有什么区别？