access_log.rb

module AccessLog
  CLF_REGEXP = /
    \A                        (?# 行頭)
    (\S+)\s                   (?# 1 address)
    (\S+)\s                   (?# 2 ident)
    (\S+)\s                   (?# 3 user)
    \[([^\]]+)\]\s            (?# 4 time)
    "(\S+)\s(\S+)\s(\S+)"\s   (?# 5 6 7 method url version)
    (\d+)\s                   (?# 8 status)
    (\d+|-)\s                 (?# 9 bytes)
    "([^"]*)"\s               (?# 10 referer)
    "([^"]*)"                 (?# 11 user_agent)
    \Z                        (?# 行末)
  /x

Entry = Struct.new(     # 解析結果を保存するためのクラス
  :address, :url, :version, :status, :byte,
  :referer, :user_agent
  )

module_function

def each_entry(file)
  file.each_line do |line|
    if entry = parse(line)
      yield(entry)
    end
  end
end

def parse(line)
  if m = CLF_REGEXP.match(line)
    return Entry.new(*m.captures)
  end
  $stderr.puts("parse failure: #{line.dump}")
  return nil
  end
end