parser_3.rb

require 'time'

class LogfileParser

  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)
    @bytes_to_skip  = File.open( 'statefile' ) { |f| f.readline.to_i } rescue 0
  end

  def search
    @log.rewind

    if 0 == @bytes_to_skip
      @log.each_line do |line|
        timestamp = line.match( TIME_REGEXP )
        next unless timestamp

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

        if current_time >= @starting_at
          @bytes_to_skip =  @log.tell
          File.open( 'statefile', 'w') { |f| f.write( @bytes_to_skip ) }
          break
        end
      end
    end
  end

  def emit &block
    search

    @log.seek( @bytes_to_skip, File::SEEK_SET)

    @log.each_line do |line|

      timestamp = line.match( TIME_REGEXP )
      next unless timestamp

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

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

      return if current_time > @ending_at
    end
  end

end

parser = LogfileParser.new( *ARGV )

parser.emit {|l| l}