Getting attribute's value in Nokogiri to extract link URLs
I have a document which look like this:
<div id="block">
<a href="http://google.com">link</a>
</div>
I can't get Nokogiri to get me th开发者_开发技巧e value of href attribute. I'd like to store the address in a Ruby variable as a string.
html = <<HTML
<div id="block">
<a href="http://google.com">link</a>
</div>
HTML
doc = Nokogiri::HTML(html)
doc.xpath('//div/a/@href')
#=> [#<Nokogiri::XML::Attr:0x80887798 name="href" value="http://google.com">]
Or if you wanna be more specific about the div:
>> doc.xpath('//div[@id="block"]/a/@href')
=> [#<Nokogiri::XML::Attr:0x80887798 name="href" value="http://google.com">]
>> doc.xpath('//div[@id="block"]/a/@href').first.value
=> "http://google.com"
doc = Nokogiri::HTML(open("[insert URL here]"))
href = doc.css('#block a')[0]["href"]
The variable href is assigned to the value of the "href" attribute for the <a> element inside the element with id 'block'. The line doc.css('#block a') returns a single item array containing the attributes of #block a. [0] targets that single element, which is a hash containing all the attribute names and values. ["href"] targets the key of "href" inside that hash and returns the value, which is a string containing the url.
Having struggled with this question in various forms, I decided to write myself a tutorial disguised as an answer. It may be helpful to others.
Starting with with this snippet:
require 'rubygems'
require 'nokogiri'
html = <<HTML
<div id="block1">
<a href="http://google.com">link1</a>
</div>
<div id="block2">
<a href="http://stackoverflow.com">link2</a>
<a id="tips">just a bookmark</a>
</div>
HTML
doc = Nokogiri::HTML(html)
extracting all the links
We can use xpath or css to find all the elements and then keep only the ones that have an href attribute:
nodeset = doc.xpath('//a') # Get all anchors via xpath
nodeset.map {|element| element["href"]}.compact # => ["http://google.com", "http://stackoverflow.com"]
nodeset = doc.css('a') # Get all anchors via css
nodeset.map {|element| element["href"]}.compact # => ["http://google.com", "http://stackoverflow.com"]
But there's a better way: in the above cases, the .compact is necessary because the searches return the "just a bookmark" element as well. We can use a more refined search to find just the elements that contain an href attribute:
attrs = doc.xpath('//a/@href') # Get anchors w href attribute via xpath
attrs.map {|attr| attr.value} # => ["http://google.com", "http://stackoverflow.com"]
nodeset = doc.css('a[href]') # Get anchors w href attribute via css
nodeset.map {|element| element["href"]} # => ["http://google.com", "http://stackoverflow.com"]
finding a specific link
To find a link within the <div id="block2">
nodeset = doc.xpath('//div[@id="block2"]/a/@href')
nodeset.first.value # => "http://stackoverflow.com"
nodeset = doc.css('div#block2 a[href]')
nodeset.first['href'] # => "http://stackoverflow.com"
If you know you're searching for just one link, you can use at_xpath or at_css instead:
attr = doc.at_xpath('//div[@id="block2"]/a/@href')
attr.value # => "http://stackoverflow.com"
element = doc.at_css('div#block2 a[href]')
element['href'] # => "http://stackoverflow.com"
find a link from associated text
What if you know the text associated with a link and want to find its url? A little xpath-fu (or css-fu) comes in handy:
element = doc.at_xpath('//a[text()="link2"]')
element["href"] # => "http://stackoverflow.com"
element = doc.at_css('a:contains("link2")')
element["href"] # => "http://stackoverflow.com"
find text from a link
And what if you want to find the text associated with a particular link? Not a problem:
element = doc.at_xpath('//a[@href="http://stackoverflow.com"]')
element.text # => "link2"
element = doc.at_css('a[href="http://stackoverflow.com"]')
element.text # => "link2"
useful references
In addition to the extensive Nokorigi documentation, I came across some useful links while writing this up:
- a handy Nokogiri cheat sheet
- a tutorial on parsing HTML with Nokogiri
- interactively test CSS selector queries
doc = Nokogiri::HTML("HTML ...")
href = doc.css("div[id='block'] > a")
result = href['href'] #http://google.com
data = '<html lang="en" class="">
<head>
<a href="https://example.com/9f40a.css" media="all" rel="stylesheet" /> link1</a>
<a href="https://example.com/4e5fb.css" media="all" rel="stylesheet" />link2</a>
<a href="https://example.com/5s5fb.css" media="all" rel="stylesheet" />link3</a>
</head>
</html>'
Here is my Try for above sample of HTML code:
doc = Nokogiri::HTML(data)
doc.xpath('//@href').map(&:value)
=> [https://example.com/9f40a.css, https://example.com/4e5fb.css, https://example.com/5s5fb.css]
document.css("#block a")["href"]
where document is the Nokogiri HTML parsed.
加载中,请稍侯......
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