A web crawler is an automated tool used to extract information from a website. Ruby is an ideal choice for implementing web crawlers with its concise syntax and powerful library support. This article will detail how to write a simple web crawler in Ruby to help you quickly get started with data scraping.

Step 1: Install Necessary Libraries

Before you start writing a crawler, you need to install some Ruby libraries to simplify the process of data scraping. The main libraries include `Nokogiri` and `HTTParty`.

```ruby

gem install nokogiri

gem install httparty

```

Step 2: Send HTTP request

First, we need to use the `HTTParty` library to send an HTTP request to get the HTML content of the target web page.

```ruby

require 'httparty'

require 'nokogiri'

url = 'https://example.com'

response = HTTParty.get(url)

html_content = response.body

```

Step 3: Parse HTML content

Next, parse the HTML content using the `Nokogiri` library to extract the required data.

```ruby

doc = Nokogiri::HTML(html_content)

```

Step 4: Extract data

Use CSS selectors or XPath to extract the required information from the parsed HTML.

```ruby

titles = doc.css('h1').map(&:text)

puts titles

```

Complete Example

Here is a complete example program to scrape all the titles of the example website:

```ruby

require 'httparty'

require 'nokogiri'

url = 'https://example.com'

response = HTTParty.get(url)

html_content = response.body

doc = Nokogiri::HTML(html_content)

titles = doc.css('h1').map(&:text)

titles.each do |title|

puts title

end

```

Implementing a web scraper in Ruby is a simple and fun process. By using powerful libraries such as `HTTParty` and `Nokogiri`, HTTP requests and HTML parsing can be easily implemented, and data scraping can be quickly performed. Whether you are a beginner or an experienced developer, Ruby is an ideal choice to help you complete crawler projects efficiently.