C#中获取系统环境变量需要用到Environment 类。
其中提供了有关当前环境和平台的信息以及操作它们的方法。该类不能被继承
以下代码得到%systemdrive%的值，即“C:”
string sPath = Environment.GetEnvironmentVariable("systemdrive");
Console.WriteLine(sPath);
更多使用方法：
//--------------获取当前程序信息
//当前程序启动的命令，字符串
Console.WriteLine("CommandLine:{0}", Environment.CommandLine);
string[] arguments = Environment.GetCommandLineArgs();
Console.WriteLine("GetCommandLineArgs:{0}", string.Join(", ", arguments));
//获取当前程序目录
Console.WriteLine("CurrentDirectory:{0}", Environment.CurrentDirectory);
//获取当前程序，工作的物理内存大小
Console.WriteLine("WorkingSet: {0}", Environment.WorkingSet);
//退出码
Console.WriteLine("ExitCode:{0}", Environment.ExitCode);
//获取当前程序是否开机启动
Console.WriteLine("HasShutdownStarted: {0}", Environment.HasShutdownStarted);
//获取当前跟踪信息
Console.WriteLine("StackTrace: '{0}'", Environment.StackTrace);
//获取换行符
Console.WriteLine("NewLine: {0} first line{0} second line{0} third line",
Environment.NewLine); //--------------获取当前用户信息
//当前用户的域名称
Console.WriteLine("UserDomainName: {0}", Environment.UserDomainName);
//当前用户是否交互
Console.WriteLine("UserInteractive: {0}", Environment.UserInteractive);
//当前用户名称
Console.WriteLine("UserName: {0}", Environment.UserName); //--------------获取当前系统信息
//获取当前计算机名称
Console.WriteLine("MachineName: {0}", Environment.MachineName);
//获取系统镜像等版本
Console.WriteLine("Version: {0}", Environment.Version.ToString());
//获取当前操作系统版本
Console.WriteLine("OSVersion: {0}", Environment.OSVersion.ToString());
//获取当前系统目录
Console.WriteLine("GetFolderPath: {0}",
Environment.GetFolderPath(Environment.SpecialFolder.System));
//获取当前计算机逻辑磁盘名称列表
String[] drives = Environment.GetLogicalDrives();
Console.WriteLine("GetLogicalDrives: {0}", String.Join(", ", drives));
//获取系统目录
String str;
String nl = Environment.NewLine;
String query = "My system drive is %SystemDrive% and my system root is %SystemRoot%";
str = Environment.ExpandEnvironmentVariables(query);
Console.WriteLine("ExpandEnvironmentVariables: {0} {1}", nl, str);
//获取系统临时文件夹
Console.WriteLine("GetEnvironmentVariable: {0} My temporary directory is {1}.", nl,
Environment.GetEnvironmentVariable("TEMP")); //--------------遍历所有信息
Console.WriteLine("GetEnvironmentVariables: ");
IDictionary environmentVariables = Environment.GetEnvironmentVariables();
foreach (DictionaryEntry de in environmentVariables)
{
Console.WriteLine(" {0} = {1}", de.Key, de.Value);
}