DouKaku?

require 'date'
require 'kconv'
WAREKI = [['明治', '1868/9/8'], ['大正', '1912/7/30'], 
  ['昭和', '1926/12/25'], ['平成', '1989/1/8']]
DATES = %w('1868/12/2' '1926/12/24' '2007/12/01' '1926/12/25'
           '1868/1/2' '1868/100/2')
wareki = WAREKI.sort{|a, b| 
  -1*(Date.parse(a[1]).year <=> Date.parse(b[1]).year)
} # => 新しい年代からマッチさせるためにソート 
DATES.each{|date_str|
  begin
    date = Date.parse(date_str)
    y0, m0, d0 = date.year, date.month, date.day
    era = wareki.each{|nengo, date_str|
      date = Date.parse(date_str)
      y1, m1, d1 = date.year, date.month, date.day
      evaluation = y0 >= y1 && (m0 > m1 or m0 == m1 && d0 >= d1)
      break [nengo, y0 - y1] if evaluation
    }
    puts "#{era[0]}#{era[1] == 0 ? '元' : era[1] + 1}年#{m0}月#{d0}日".tosjis
  rescue
    puts '範囲外'.tosjis
    next
  end
}

#!/usr/local/bin/ruby -Ke
require 'time'

class DateRange < Range
  attr_reader :infinit
  def initialize(first, last, exclude_end = false)
    super
    @infinit = true if first > last
  end

  def ===(other)
    return super unless @infinit
    return true if self.first <= other
    return false
  end
end

def acceptable?(date, y, m, d)
  unless (0 < m and m < 13) and (0 < d and d < 32) and
         (date >= '1873/01/01')
    return false
  end
  return true
end

def usage
  puts "usage: #{File.basename($0)} <date>"
end

class DateOutOfRange < Exception; end

era = [['明治', ['1868/01/25', '1912/07/30']],
       ['大正', ['1912/07/30', '1926/12/25']],
       ['昭和', ['1926/12/25', '1989/01/07']],
       ['平成', ['1989/01/08', '1970/01/01']]].
      map {|name, r| [name, DateRange.new(*r)] }
begin
  date = ARGV[0]
  y, m, d = %r!(\d+)[/-](\d+)[/-](\d+)!.match(date).to_a[1..-1].map {|x| x.to_i}
  date = "%04d/%02d/%02d" % [y, m, d]
  raise DateOutOfRange unless acceptable?(date, y, m, d)
  result = era.select {|_, r| r === date}.
               map {|name, r| [name, y - r.first.split('/')[0].to_i + 1] }.
               map {|name, y| "%s%d年%d月%d日" % [name, y, m, d] }
  raise DateOutOfRange if result.empty?
  puts result.join(' ')
rescue DateOutOfRange
  puts '範囲外'
rescue
  usage
  exit(1)
end

#!/usr/bin/env ruby -Ku

require 'date'

def seireki2wareki(date = Date.today)
  case
  when date > Date.new(1989, 1, 7)
    "平成#{date.year - 1988}年#{date.month}月#{date.day}日"
  when date == Date.new(1989, 1, 7)
    '昭和64年1月7日 平成1年1月7日'
  when date > Date.new(1926, 12, 25)
    "昭和#{date.year - 1925}年#{date.month}月#{date.day}日"
  when date == Date.new(1926, 12, 25)
    '大正15年12月25日 昭和1年12月25日'
  when date > Date.new(1912, 7, 30)
    "大正#{date.year - 1911}年#{date.month}月#{date.day}日"
  when date == Date.new(1912, 7, 30)
    '明治45年7月30日 大正1年7月30日'
  when date > Date.new(1868, 9, 8)
    "明治#{date.year - 1867}年#{date.month}月#{date.day}日"
  else
    '範囲外'
  end
end

if __FILE__ == $0
  begin
    if ARGV.empty?
      puts seireki2wareki
    else
      puts seireki2wareki(Date.parse(ARGV.shift))
    end
  rescue
    puts '範囲外'
  end
end

require 'date'

DAYS = [Date.parse('1873/1/1'), Date.parse('1912/7/30'), Date.parse('1926/12/25'), Date.parse('1989/1/8')]
GENGO = ['明治', '大正', '昭和', '平成']

def format_date(d, i)
  raise if d < DAYS[0]
   d = d + 365 * 6 + 1 if i <= 1 #明治用のオフセット
  return "#{GENGO[i != 0 ? i - 1 : i]}#{d.year - DAYS[i - 1].year + 1}年#{d.month}月#{d.day}日"
end

begin
  d = Date.parse(ARGV[0])
  days = DAYS.push(d).sort
  i = days.index(d)
  puts (days.uniq.size == 4 && i != 0 ? format_date(d, i) << ' ' << format_date(d, i + 1) : format_date(d, i))
rescue
  puts '範囲外'
end