Naive log watcher for Rails

tail_rails_log.rb

# ruby tail_rails_log.rb log/development.log
require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'file-tail'
end

puts 'Watching for errors: ' + ARGV[0]
lines_to_catch = 0
start_lines = []

File.open(ARGV[0]) do |log|
  log.extend(File::Tail)

  log.backward(1).tail do |log_line|
    if lines_to_catch.positive?
      puts log_line
      lines_to_catch -= 1
      puts '--------------<<<<<<<' if lines_to_catch.zero?
    end

    if log_line =~ /^Started/
      start_lines = []
      start_lines << log_line
    end

    if log_line =~ /^Processing/
      start_lines << log_line
    end

    if log_line =~ /Completed 500/ || log_line =~/Error/
      lines_to_catch = 15
      puts '>>>>>>>--------------'
      start_lines.each { |l| puts l }
      puts '---------------------'
      puts log_line
      puts '>-------------------<'
    end
  end
end
# >>>>>>>--------------
# Started GET "/asfd" for 127.0.0.1 at 2019-11-15 23:36:50 +0200
# ---------------------
# ActionController::RoutingError (No route matches [GET] "/asfd"):
# >-------------------<
  
# actionpack (5.2.2) lib/action_dispatch/middleware/debug_exceptions.rb:65:in `call'
# rack-contrib (2.1.0) lib/rack/contrib/response_headers.rb:17:in `call'
# meta_request (0.6.0) lib/meta_request/middlewares/headers.rb:16:in `call'
# web-console (3.7.0) lib/web_console/middleware.rb:135:in `call_app'
# web-console (3.7.0) lib/web_console/middleware.rb:30:in `block in call'
# web-console (3.7.0) lib/web_console/middleware.rb:20:in `catch'
# web-console (3.7.0) lib/web_console/middleware.rb:20:in `call'
# actionpack (5.2.2) lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
# railties (5.2.2) lib/rails/rack/logger.rb:38:in `call_app'
# railties (5.2.2) lib/rails/rack/logger.rb:26:in `block in call'
# activesupport (5.2.2) lib/active_support/tagged_logging.rb:71:in `block in tagged'
# activesupport (5.2.2) lib/active_support/tagged_logging.rb:28:in `tagged'
# activesupport (5.2.2) lib/active_support/tagged_logging.rb:71:in `tagged'
# railties (5.2.2) lib/rails/rack/logger.rb:26:in `call'
# --------------<<<<<<<