如何使用Ruby和Nokogiri解析谷歌图像URL

使用正则表达式的问题是您对URL中参数的顺序了解太多。如果顺序发生变化，或者&消失，正则表达式将不起作用。

相反，解析URL，然后将值拆分出来：

# encoding: UTF-8
require 'nokogiri'
require 'cgi'
require 'uri'
doc = Nokogiri::HTML.parse('<a href="http://www.google.com/imgres?imgurl=http://www.trendytree.com/old-world-christmas/images/20031chapel20031-silent-night-chapel.jpg&amp;imgrefurl=http://www.trendytree.com/old-world-christmas/silent-night-chapel-20031-christmas-ornament-old-world-christmas.html&amp;usg=__YJdf3xc4ydSfLQa9tYnAzavKHYQ=&amp;h=400&amp;w=400&amp;sz=58&amp;hl=en&amp;start=19&amp;zoom=1&amp;tbnid=ajDcsGGs0tgE9M:&amp;tbnh=124&amp;tbnw=124&amp;ei=qagfUbXmHKfv0QHI3oG4CQ&amp;itbs=1&amp;sa=X&amp;ved=0CE4QrQMwEg"><img height="124" width="124" src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRLy5inpSdHxWuE7z3QSZw35JwN3upbBaLr11LR25noTKbSMn9-qrySSg"></a><br><cite title="trendytree.com">trendytree.com</cite><br>Silent Night Chapel <b>20031</b><br>400 × 400 - 58k - jpg</td>')
img_url = doc.search('a').each do |a|
  query_params = CGI::parse(URI(a['href']).query) 
  puts query_params['imgurl']
end

哪个输出：

http://www.trendytree.com/old-world-christmas/images/20031chapel20031-silent-night-chapel.jpg

同时使用URI和CGI是因为URI的decode_www_form在尝试解码查询时会引发异常。

众所周知，我还可以使用以下方法将查询字符串解码为哈希：

Hash[URI(a['href']).query.split('&').map{ |p| p.split('=') }]

这将返回：

｛"imgurl"=>"http://www.trendytree.com/old-world-christmas/images/20031chapel20031-silent-night-chapel.jpg"，"imgrefurl"=>"http://www.trendytree.com/old-world-christmas/silent-night-chapel-20031-christmas-ornament-old-world-christmas.html"，"usg"=>"__YJdf3xc4ydSfLQa9tYnAzavKHYQ"，"h"=>"400"，"w"=>"400"，"sz"=>"58"，"hl"=>"en"，"start"=>"19"，"zoom"=>"1"，"tbnid"=>"ajDcsGGs0tgE9M:"，"tbnh"=>"124"，"tbnw"=>"124"，"ei"=>"qagfUbXmHKfv0QHI3oG4CQ"，"itbs"=>"1"，"sa"=>"X"，"ved"=>"0CE4QrQMwEg"｝

要获得您想要的所有img URL，请执行

# get all links
url = 'some-google-images-url'
links = Nokogiri::HTML( open(url) ).css('a')
# get regex match or nil on desired img
img_urls = links.map {|a| a['href'][/imgurl=(.*?)&/, 1] }
# get rid of nils
img_urls.compact

您想要的正则表达式是/imgurl=(.*?)&/，因为您想要imgurl=和&之间的非贪婪匹配，否则贪婪的.*将把所有内容都带到字符串中的最后一个&。