How do I scrape data from a website that requires login using Ruby?

To scrape data from a website that requires login using Ruby, you need to simulate the login process programmatically. You can use the Mechanize gem for this purpose, which is a library used for automating interaction with websites.

First, make sure you have the Mechanize gem installed. You can install it using the following command:

gem install mechanize

Here is a step-by-step guide on how to scrape data from a website that requires login:

1. Require the Mechanize Gem

At the beginning of your Ruby script, require the Mechanize gem:

require 'mechanize'

2. Create a Mechanize Agent

Create a new instance of the Mechanize agent which will handle the requests:

agent = Mechanize.new

3. Load the Login Page

Use the agent to fetch the login page:

login_page = agent.get('https://example.com/login')

4. Fill in the Login Form

Identify the form fields for the username and password, and submit the form:

login_form = login_page.form_with(:action => '/session') do |form|
  form.field_with(:name => 'username').value = 'your_username'
  form.field_with(:name => 'password').value = 'your_password'
end

5. Submit the Login Form

Submit the form to perform the login:

dashboard_page = agent.submit(login_form)

6. Access Protected Pages

After logging in, you can access protected pages and scrape data from them:

protected_page = agent.get('https://example.com/protected_page')
puts protected_page.body

7. Parse the Data

Use Nokogiri (which is bundled with Mechanize) to parse the HTML and extract information:

require 'nokogiri'

page = Nokogiri::HTML(protected_page.body)
items = page.css('div.item') # CSS selector for the items you want to scrape

items.each do |item|
  title = item.at_css('h2.title').text
  description = item.at_css('p.description').text
  # Extract other data as needed
  puts "Title: #{title}, Description: #{description}"
end

Full Example

Here's a full example that combines all the steps:

require 'mechanize'

# Initialize Mechanize Agent
agent = Mechanize.new

# Fetch the login page
login_page = agent.get('https://example.com/login')

# Fill in and submit the login form
login_form = login_page.form_with(:action => '/session') do |form|
  form.field_with(:name => 'username').value = 'your_username'
  form.field_with(:name => 'password').value = 'your_password'
end
dashboard_page = agent.submit(login_form)

# After login, access a protected page
protected_page = agent.get('https://example.com/protected_page')

# Parse the page with Nokogiri
require 'nokogiri'
page = Nokogiri::HTML(protected_page.body)
items = page.css('div.item')

# Scrape the items
items.each do |item|
  title = item.at_css('h2.title').text
  description = item.at_css('p.description').text
  # Extract other data as needed
  puts "Title: #{title}, Description: #{description}"
end

Remember to replace https://example.com/login, https://example.com/protected_page, your_username, and your_password with the actual URL and credentials for the website you want to scrape.

Note on Ethical and Legal Considerations: Before scraping any website, it's important to review the site's robots.txt file and Terms of Service to understand any restrictions on automated access or data scraping. Additionally, you should ensure that your scraping activities are not violating any laws or regulations. Be respectful of the website's resources and avoid making excessive requests that could impact the website's performance.