キーに姓、バリューに名を格納したハッシュに yasuhiro と引数を渡 すことで onishi と返すスクリプト

#!/usr/bin/env ruby

staff={
  "kondo" => "junya",
  "ito" => "naoya",
  "onishi" =>  "yasuhiro",
  "danjou" => "nobuo",
  "minowa" => "higepon"
}

hatena=ARGV.shift
if staff.key?(hatena) then
    p staff[hatena]
end