rubyでカタカナをひらがなに変換

jocodeが必要。

require 'jcode'
str="アイウエオ"
str2= str.tr("ァ-ン","ぁ-ん")
puts str2

require 'jcode'
a=File.open(ARGV[0]);a.each{|str|

str=str.gsub (/lya/,"ャ")
str=str.gsub (/lyu/,"ュ")
str=str.gsub (/lyo/,"ョ")
str=str.gsub (/lwa/,"ヮ")
str=str.gsub (/ltu/,"ッ")
str=str.gsub (/va/,"ヴ")
str=str.gsub (/lka/,"ヵ")
str=str.gsub (/lke/,"ヶ")
str=str.gsub (/_a/,"ア")
str=str.gsub (/_i/,"イ")
str=str.gsub (/_u/,"ウ")
str=str.gsub (/_e/,"エ")
str=str.gsub (/_o/,"オ")
str=str.gsub (/ka/,"カ")
str=str.gsub (/ki/,"キ")
str=str.gsub (/ku/,"ク")
str=str.gsub (/ke/,"ケ")
str=str.gsub (/ko/,"コ")
str=str.gsub (/sa/,"サ")
str=str.gsub (/si/,"シ")
str=str.gsub (/su/,"ス")
str=str.gsub (/se/,"セ")
str=str.gsub (/so/,"ソ")
str=str.gsub (/ta/,"タ")
str=str.gsub (/ti/,"チ")
str=str.gsub (/tu/,"ツ")
str=str.gsub (/te/,"テ")
str=str.gsub (/to/,"ト")
str=str.gsub (/na/,"ナ")
str=str.gsub (/ni/,"ニ")
str=str.gsub (/nu/,"ヌ")
str=str.gsub (/ne/,"ネ")
str=str.gsub (/no/,"ノ")
str=str.gsub (/ha/,"ハ")
str=str.gsub (/hi/,"ヒ")
str=str.gsub (/hu/,"フ")
str=str.gsub (/he/,"へ")
str=str.gsub (/ho/,"ホ")
str=str.gsub (/ma/,"マ")
str=str.gsub (/mi/,"ミ")
str=str.gsub (/mu/,"ム")
str=str.gsub (/me/,"メ")
str=str.gsub (/mo/,"モ")
str=str.gsub (/ya/,"ヤ")
str=str.gsub (/yu/,"ユ")
str=str.gsub (/yo/,"ヨ")
str=str.gsub (/ra/,"ラ")
str=str.gsub (/ri/,"リ")
str=str.gsub (/ru/,"ル")
str=str.gsub (/re/,"レ")
str=str.gsub (/ro/,"ロ")
str=str.gsub (/wa/,"ワ")
str=str.gsub (/wo/,"ヲ")
str=str.gsub (/nn/,"ン")
str=str.gsub (/la/,"ァ")
str=str.gsub (/li/,"ィ")
str=str.gsub (/lu/,"ゥ")
str=str.gsub (/le/,"ェ")
str=str.gsub (/lo/,"ォ")
str=str.gsub (/ga/,"ガ")
str=str.gsub (/gi/,"ギ")
str=str.gsub (/gu/,"グ")
str=str.gsub (/ge/,"ゲ")
str=str.gsub (/go/,"ゴ")
str=str.gsub (/za/,"ザ")
str=str.gsub (/zi/,"ジ")
str=str.gsub (/zu/,"ズ")
str=str.gsub (/ze/,"ゼ")
str=str.gsub (/zo/,"ゾ")
str=str.gsub (/da/,"ダ")
str=str.gsub (/di/,"ヂ")
str=str.gsub (/du/,"ヅ")
str=str.gsub (/de/,"デ")
str=str.gsub (/do/,"ド")
str=str.gsub (/ba/,"バ")
str=str.gsub (/bi/,"ビ")
str=str.gsub (/bu/,"ブ")
str=str.gsub (/be/,"ベ")
str=str.gsub (/bo/,"ボ")
str=str.gsub (/pa/,"パ")
str=str.gsub (/pi/,"ピ")
str=str.gsub (/pu/,"プ")
str=str.gsub (/pe/,"ぺ")
str=str.gsub (/po/,"ポ")
str=str.gsub (/lya/,"ャ")
str=str.gsub (/lyu/,"ュ")
str=str.gsub (/lyo/,"ョ")
str=str.gsub (/lwa/,"ヮ")
str=str.gsub (/ltu/,"ッ")
str=str.gsub (/va/,"ヴ")
str=str.gsub (/lka/,"ヵ")
str=str.gsub (/lke/,"ヶ")
puts str.tr("ァ-ン","ぁ-ん")}