How do I avoid getting banned while scraping with Ruby?

Web scraping can sometimes be seen as a grey area, especially when it comes to the terms of service of many websites. To avoid getting banned while scraping with Ruby, you should follow ethical scraping practices and respect the website's rules and regulations. Here are several tips to help you avoid being banned:

1. Respect robots.txt: Most websites have a robots.txt file that specifies which parts of the site should not be accessed by bots. Make sure your scraper respects these rules.

2. User-Agent: Change your User-Agent to mimic a real web browser or use a legitimate one. Some sites block requests that don't come from standard web browsers.

3. Request Headers: Use proper request headers and mimic them as close as possible to what a regular browser would send.

4. Limit Request Rate: Do not bombard the website with a large number of requests in a short period. Implement delays between requests or randomize intervals to mimic human behavior.

5. Use Proxies: If you're doing large-scale scraping, you might want to use proxies to avoid your IP address getting banned. Rotate your requests through different proxy servers.

6. Caching: Cache responses locally where possible, to avoid making unnecessary requests for the same resources.

7. Handle Errors Gracefully: If you encounter a 4xx or 5xx error, your script should handle it properly, possibly by backing off for a while before trying again.

8. Session Management: If the website requires login, make sure you manage your sessions and cookies as a browser would.

9. JavaScript Rendering: Some sites load data with JavaScript. You might need to use a tool like Selenium or Puppeteer, which can handle JavaScript-rendered content.

10. Scrape During Off-Peak Hours: Try to schedule your scraping during the website's off-peak hours.

11. Legal Compliance: Always check the website’s Terms of Service to ensure you are not violating any terms.

Below is a Ruby example using the Mechanize gem to demonstrate some of these practices:

require 'mechanize'

# Create a new Mechanize agent
agent = Mechanize.new

# Set a custom User-Agent
agent.user_agent_alias = 'Windows Mozilla'

# Respect robots.txt
agent.robots = true

# Implement delay between requests
agent.history_added = Proc.new { sleep 0.5 }

# Start scraping
begin
  page = agent.get("http://example.com/")

  # Do your scraping tasks...

rescue Mechanize::ResponseCodeError => e
  puts "Received a response code error: #{e.response_code}"
  # Handle error, possibly retry after a delay
rescue => e
  puts "An error occurred: #{e.message}"
  # Handle other errors
end

In this example, we've set a custom User-Agent, respected the robots.txt file, added a delay between requests, and handled exceptions gracefully.

Lastly, remember that while these practices can help avoid bans, they do not guarantee that aggressive scraping won't be detected, and they should be used responsibly and ethically. Always prioritize the website's rules and the legality of your actions.