c# - Environment.ExpandEnvironmentVariables がすべての変数で機能しない

Question

メソッドが、などのEnvironment.ExpandEnvironmentVariables()一部のシステム変数の値を返さないことに気付きました...なぜですか?%date%%time%%homeshare%

Answer 1

%HOMESHARE%単に定義されていない可能性があります (すべての状況で定義されているわけではありません)。%DATE%および%TIME%は、私の知る限り、外部では使用できない動的変数ですCMD(たとえば%CD%およびについても同様です%ERRORLEVEL%)。

Answer 2

@Ansgar WiechersCMD.EXEはもちろん正しいです。特定の変数の（一部）も置き換えようとする次の関数にコードを提供すると思いました。

    public static string ExpandEnvironmentVariables(string str)
    {
        // Environment.ExpandEnvironmentVariables() does this as well, but we don't rely on that.
        if (str == null)
            throw new ArgumentNullException("str");

        // First let .NET Fx version do its thing, because then:
        //
        // - Permission checks, etc. will already be done up front.
        // - Should %CD% already exists as a user defined variable, it will already be replaced,
        //   and we don't do it by the CurrentDirectory later on. This behavior is consistent with
        //   what CMD.EXE does.
        //   Also see http://blogs.msdn.com/b/oldnewthing/archive/2008/09/26/8965755.aspx.
        //  
        str = Environment.ExpandEnvironmentVariables(str);

        // The following is rather expensive, so a quick check if anything *could* be required at all
        // seems to be warrented.
        if (str.IndexOf('%') != -1)
        {
            const StringComparison comp = StringComparison.OrdinalIgnoreCase;
            var invariantCulture = CultureInfo.InvariantCulture;
            var now = DateTime.Now;

            str = str.Replace("%CD%", Environment.CurrentDirectory, comp);
            str = str.Replace("%TIME%", now.ToString("T") + "," + now.ToString("ff"), comp);
            str = str.Replace("%DATE%", now.ToString("d"), comp);
            str = str.Replace("%RANDOM%", s_random.Next(0, Int16.MaxValue).ToString(invariantCulture), comp);

            // Debatable, but we replace them anyway to make sure callers don't "crash" because
            // them not being unexpanded, and becase we "can".

            str = str.Replace("%CMDEXTVERSION%", "2", comp); // This is true at least on XP to Server 2008R2
            str = str.Replace("%CMDCMDLINE%", Environment.CommandLine, comp);

            uint nodeNumber;
            if (!NativeMethods.GetNumaHighestNodeNumber(out nodeNumber))
            {
                nodeNumber = 0;
            }

            str = str.Replace("%HIGHESTNUMANODENUMBER%", nodeNumber.ToString(invariantCulture), comp);
        }

        return str;
    }

P/Invokeの定義GetNumaHighestNodeNumberは次のとおりです。

    [DllImport(KernelDll)]
    [return: MarshalAsAttribute(UnmanagedType.Bool)]
    public static extern bool GetNumaHighestNodeNumber([Out] out uint   HighestNodeNumber);