Ruby Win32註冊表：當查找不存在的註冊表項時，系統找不到指定的文件

Question

我正在寫一個ruby函數以從給定的DisplayName獲取UninstallString。當我給它一個現有的DisplayName來查找時，我的函數只能成功運行，當我給出不存在的東西時它崩潰。我不確定哪個變量需要檢查什麼條件（nil？空？），以便我可以向腳本中拋出一個異常，輸出'not found'消息而不是崩潰？

require 'win32/registry' 

def get_uninstallstring(app_name) 

    paths = [ "Software\\Microsoft\\Windows\\CurrentVersion\\Uninstall", 
      "Software\\Wow6432Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall", 
      "Software\\Wow6464Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall" ] 
    access_type = Win32::Registry::KEY_ALL_ACCESS 

    paths.each do |path|   # This is line 9 
    Win32::Registry::HKEY_LOCAL_MACHINE.open(path, access_type) do |reg| 
     reg.each_key do |key| 
     k = reg.open(key) 
     app = k['DisplayName'] rescue nil 
     if app == app_name 
      str = k['UninstallString'] rescue nil 
      return str 
     end 
     end 
    end 
    end 
    return false 
end 

puts get_uninstallstring("ABC") # This is line 24 

以下是錯誤輸出：

C:/ruby/1.9.1/win32/registry.rb:385:in `open': The system cannot find the file specified. (Win32::Registry::Error) 
     from C:/heliopolis/opscode/chef/embedded/lib/ruby/1.9.1/win32/registry.rb:496:in `open' 
     from test.rb:10:in `block in get_uninstallstring' 
     from test.rb:9:in `each' 
     from test.rb:9:in `get_uninstallstring' 
     from test.rb:24:in `<main>' 

Answer 1

於是我找到了解決自己。我必須編寫另一個函數來檢查密鑰是否存在於給定的路徑中，然後才能真正獲得它的值。

def key_exists?(path) 
    begin 
    Win32::Registry::HKEY_LOCAL_MACHINE.open(path, ::Win32::Registry::KEY_READ) 
    return true 
    rescue 
    return false 
    end 
end 

，這裏是修改get函數：

paths.each do |path| 
    if key_exists?(path) 
     Win32::Registry::HKEY_LOCAL_MACHINE.open(path, access_type) do |reg| 
     reg.each_key do |key| 
      k = reg.open(key) 
      app = k['DisplayName'] rescue nil 
      if app == app_name 
     return k['UninstallString'] rescue nil 
      end 
     end 
     end 
    else 
     return false 
    end 
    end