parser_2.rb

require 'time'

class LogfileParser

  # Regexp to match the timestamps in the apache common log format
  TIME_REGEXP   = /\[\d{2}\/\w{3}\/\d{4}\:\d{2}:\d{2}:\d{2}\s.{5}\]/

  def initialize path, starting_at
    raise ArgumentError unless File.exists?( path )

    @log            = File.open( path )
    @starting_at    = Time.parse( starting_at )
    @ending_at      = (@starting_at + 300)

    # Read line number from state file
    @lines_to_skip  = File.open( 'statefile' ) { |f| f.readline.to_i } rescue 0
  end

  def emit &block
    @log.each_line do |line|

      # skip lines
      next unless @log.lineno >= @lines_to_skip.to_i

      next unless timestamp = line.match( TIME_REGEXP )

      current_time = Time.parse( timestamp[0].sub(":", " ") )

      if current_time >= @starting_at && current_time <= @ending_at
        yield line
      end

      # Write new line number to statefile
      if current_time > @ending_at
        File.open( 'statefile', 'w') { |f| f.write( @log.lineno ) }
        break
      end
    end
  end

end

parser = LogfileParser.new( *ARGV )

parser.emit {|l| puts l}