Nokogiri is a popular Ruby library used for parsing HTML and XML. When you combine Nokogiri with regular expressions, you can perform powerful text processing on the content of web pages or XML documents.
Here's how to use Nokogiri in conjunction with regular expressions:
Install Nokogiri: If you haven't already installed Nokogiri, you can do so using the following command:
gem install nokogiriRequire Nokogiri: In your Ruby script, include Nokogiri by adding the following line at the top of your file:
require 'nokogiri'Parse the Document: Use Nokogiri to parse an HTML or XML document. You can load the document from a string, a file, or directly from a website.
# Parse HTML from a string html = "<html><body><p>Hello, world!</p></body></html>" doc = Nokogiri::HTML(html) # or parse HTML from a file doc = File.open("index.html") { |f| Nokogiri::HTML(f) } # or parse HTML from the web (requires 'open-uri') require 'open-uri' doc = Nokogiri::HTML(URI.open("http://www.example.com"))Use Regular Expressions: After parsing the document, you can use Nokogiri's CSS or XPath selectors to find nodes, and then apply regular expressions to the content or attributes of those nodes.
# Find all <p> tags and print their content if it matches a regular expression doc.css('p').each do |p_node| if p_node.content =~ /Hello, \w+!/ puts p_node.content end end # Find nodes with 'id' attribute matching a pattern doc.xpath('//*').each do |node| if node['id'] && node['id'].match(/\Apost-\d+\z/) puts node['id'] end end
Here's a more concrete example with explanations:
require 'nokogiri'
require 'open-uri'
# Load the HTML document from a URL
doc = Nokogiri::HTML(URI.open("http://www.example.com"))
# Let's say we want to find all the links that have 'example' in their href attributes
regex = /example/
# Use Nokogiri to find all 'a' elements, then use Ruby's Enumerable#select to filter them with regex
matching_links = doc.css('a').select { |link| link['href'] =~ regex }
# Output the href attributes of the matching links
matching_links.each do |link|
puts link['href']
end
In this example, we load an HTML document from a URL using Nokogiri. Then, we specify a regular expression to match 'href' attributes that contain the word "example". We then iterate over all 'a' elements and select those that match our regular expression. Finally, we output the 'href' attributes of those links.
Remember that regular expressions can be quite powerful, but they can also be complex and difficult to maintain. Use them judiciously and always test them thoroughly to ensure they match exactly what you intend. When possible, prefer using Nokogiri's built-in CSS and XPath selectors, as they are often more readable and maintainable than complex regular expressions.
