apache_log.rb

#!/usr/bin/env ruby

LOG_ITEMS = %w(ip_address ident_user_name authenticate_user_name access_date request_line status_code forwarding_byte caller_url user_agent).each

class LogParser
  def initialize(logs)
    @logs = logs.chomp
    @result = {}
    @start_idx = 0
  end

  def parse
    @logs.each_char.with_index do |char, idx|
      case char
      when '['
        @start_idx = idx
        @bracket = :start
      when ']'
        @bracket = :end
      when '"'
        if @quote
          @quote = :end
        else
          @start_idx = idx
          @quote = :start
        end
      when ' '
        next if @bracket == :start || @quote == :start

        store(@start_idx, idx - @start_idx)
        @start_idx = idx + 1
      end
    end

    store(@start_idx, @logs.length)

    @result
  end

  def store(nth, len)
    @result[LOG_ITEMS.next] = @logs[nth, len]

    @bracket = @quote = nil
  end
end

p LogParser.new(ARGF.readlines[0]).parse