Japanese Era Calendar Scheme

era.rb

#-*- encoding:utf-8 -*-
require 'date'

date=Date.parse ARGV[0]

eras = [
    [Date.parse('1989-01-08'), '平成'],
    [Date.parse('1926-12-25'), '昭和'],
    [Date.parse('1912-07-30'), '大正'],
    [Date.parse('1868-09-08'), '明治'],
]

era_start, era = eras.find { |start, era| start <= date }

print "#{era}#{date.year-era_start.year+1}年#{date.month}月#{date.day}日\n"

era2.rb

#-*- encoding:utf-8 -*-
require 'date'

date=Date.parse ARGV[0]

eras = [
    [[1989, 1, 8], '平成'],
    [[1926,12,25], '昭和'],
    [[1912, 7,30], '大正'],
    [[1868, 9, 8], '明治'],
]

era_start, era = eras.find do |start, era| Date.new(*start) <= date end
era_start_year=era_start.first

print "#{era}#{date.year-era_start_year+1}年#{date.month}月#{date.day}日\n"

era3.rb

#-*- encoding:utf-8 -*-

date=ARGV[0]
dateexp=/^(\d{4})-(\d\d)-(\d\d)$/

match = date.match dateexp
raise "Unparsable date: #{date}" unless match
year, month, day = match[1].to_i, match[2], match[3]
# year,month,day=ARGV[0].match(dateexp)do |match|
#   raise "Unparsable date: #{date}" unless match
#   [match[1],match[2],match[3]].map &:to_i
# end

#year,month,day=date.split("-").map &:to_i

eras = [
    ['1989-01-08', '平成'],
    ['1926-12-25', '昭和'],
    ['1912-07-30', '大正'],
    ['1868-09-08', '明治'],
]

era_start, era = eras.find { |start, era| start <= date }

era_start_year = era_start.match(/^\d{4}/)[0].to_i
# era_start_year = era_start.match(/^\d{4}/).to_s.to_i
# era_start_year = era_start[0,4].to_i
# era_start_year = era_start.split("-").first.to_i


printf("%s%s年%s月%s日\n", era, (year-era_start_year+1).to_s, month, day)
# print "#{era}#{year-era_start_year+1}年#{month}月#{day}日\n"

era4.rb

#-*-encoding:utf-8-*-
a,b,c=ARGV[0].split("-").map &:to_i
d=(a-=1911)*372+b*31+c
print "明治大正昭和平成"[i=d<619?0:d<5977?2:d<29055?4:6,2]+"#{a-[-44,0,14,77][i/2]}年#{b}月#{c}日"