Environment.GetEnvironmentVariable 方法

定义

命名空间:

System

程序集:

System.Runtime.dll

检索环境变量的值。

重载

GetEnvironmentVariable(String)	从当前进程检索环境变量的值。
GetEnvironmentVariable(String, EnvironmentVariableTarget)	从当前进程或者从当前用户或本地计算机的 Windows 操作系统注册表项检索环境变量的值。

GetEnvironmentVariable(String)

Source:

Environment.cs

从当前进程检索环境变量的值。

C#

public static string? GetEnvironmentVariable (string variable);

参数

variable

String

环境变量的名称。

返回

String

variable 指定的环境变量的值；或者如果找不到环境变量，则返回 null。

例外

ArgumentNullException

variable 为 null。

SecurityException

调用方没有执行此操作所需的权限。

示例

下面的示例使用 GetEnvironmentVariable 方法检索 windir 环境变量，其中包含 Windows 目录的路径。

C#

using System;
using System.IO;

public class Example
{
   public static void Main()
   {
      if (Environment.OSVersion.Platform == PlatformID.Win32NT)
      {
         // Change the directory to %WINDIR%
         Environment.CurrentDirectory = Environment.GetEnvironmentVariable("windir");
         DirectoryInfo info = new DirectoryInfo(".");

         Console.WriteLine("Directory Info:   " + info.FullName);
      }
      else
      {
         Console.WriteLine("This example runs on Windows only.");
      }
   }
}
// The example displays output like the following on a .NET implementation running on Windows:
//        Directory Info:   C:\windows
// The example displays the following output on a .NET implementation on Unix-based systems:
//        This example runs on Windows only.

以下示例尝试从进程环境块检索名为 Test1 的环境变量的值。 如果变量不存在，示例将创建它并检索其值。 该示例显示 变量的值。 如果示例创建了 变量，则它还使用 枚举的每个成员EnvironmentVariableTarget调用 GetEnvironmentVariables(EnvironmentVariableTarget) 方法，以确定只能从当前进程环境块检索该变量。 最后，如果示例创建了变量，则会将其删除。

C#

using System;

public class Example
{
   public static void Main()
   {
      string value;
      bool toDelete = false;

      // Check whether the environment variable exists.
      value = Environment.GetEnvironmentVariable("Test1");
      // If necessary, create it.
      if (value == null)
      {
         Environment.SetEnvironmentVariable("Test1", "Value1");
         toDelete = true;

         // Now retrieve it.
         value = Environment.GetEnvironmentVariable("Test1");
      }
      // Display the value.
      Console.WriteLine($"Test1: {value}\n");

      // Confirm that the value can only be retrieved from the process
      // environment block if running on a Windows system.
      if (Environment.OSVersion.Platform == PlatformID.Win32NT)
      {
         Console.WriteLine("Attempting to retrieve Test1 from:");
         foreach (EnvironmentVariableTarget enumValue in
                           Enum.GetValues(typeof(EnvironmentVariableTarget))) {
            value = Environment.GetEnvironmentVariable("Test1", enumValue);
            Console.WriteLine($"   {enumValue}: {(value != null ? "found" : "not found")}");
         }
         Console.WriteLine();
      }

      // If we've created it, now delete it.
      if (toDelete) {
         Environment.SetEnvironmentVariable("Test1", null);
         // Confirm the deletion.
         if (Environment.GetEnvironmentVariable("Test1") == null)
            Console.WriteLine("Test1 has been deleted.");
      }
   }
}
// The example displays the following output if run on a Windows system:
//      Test1: Value1
//
//      Attempting to retrieve Test1 from:
//         Process: found
//         User: not found
//         Machine: not found
//
//      Test1 has been deleted.
//
// The example displays the following output if run on a Unix-based system:
//      Test1: Value1
//
//      Test1 has been deleted.

注解

有关此 API 的详细信息，请参阅 Environment.GetEnvironmentVariable 的补充 API 备注。

另请参阅

• GetEnvironmentVariables()
• SetEnvironmentVariable(String, String)
• EnvironmentVariableTarget

GetEnvironmentVariable(String, EnvironmentVariableTarget)

Source:

Environment.cs

从当前进程或者从当前用户或本地计算机的 Windows 操作系统注册表项检索环境变量的值。

C#

public static string? GetEnvironmentVariable (string variable, EnvironmentVariableTarget target);

参数

variable

String

环境变量名。

target

EnvironmentVariableTarget

EnvironmentVariableTarget 值之一。 仅在 Process 运行在类似 Unix 的系统上的 .NET 上受支持。

返回

String

variable 和 target 参数指定的环境变量的值；或者如果找不到环境变量，则返回 null。

例外

ArgumentNullException

variable 为 null。

ArgumentException

target 不是有效的 EnvironmentVariableTarget 值。

SecurityException

调用方没有执行此操作所需的权限。

示例

以下示例为 EnvironmentVariableTarget.Process、 EnvironmentVariableTarget.User和 Machine 目标创建环境变量，检查操作系统注册表是否包含用户和计算机环境变量，然后删除环境变量。 由于类似 Unix 的系统上的 .NET 不支持每用户和每计算机环境变量，因此仅 SetEnvironmentVariable(String, String) 和 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 值为 EnvironmentVariableTarget.Process 成功将环境变量存储到进程环境块。

C#

using System;
using System.Collections;
using Microsoft.Win32;

class Sample
{
    public static void Main()
    {
        // Environment variable names for default, process, user, and machine targets.
        string defaultEnvVar = nameof(defaultEnvVar);
        string processEnvVar = nameof(processEnvVar);
        string userEnvVar = nameof(userEnvVar);
        string machineEnvVar = nameof(machineEnvVar);

        string dft = nameof(dft);
        string process = nameof(process);
        string user = nameof(user);
        string machine = nameof(machine);

        // Set the environment variable for each target.
        Console.WriteLine("Setting environment variables for each target...\n");
        // The default target (the current process).
        Environment.SetEnvironmentVariable(defaultEnvVar, dft);
        // The current process.
        Environment.SetEnvironmentVariable(processEnvVar, process,
                                           EnvironmentVariableTarget.Process);
        // The current user.
        Environment.SetEnvironmentVariable(userEnvVar, user,
                                           EnvironmentVariableTarget.User);
        // The local machine.
        Environment.SetEnvironmentVariable(machineEnvVar, machine,
                                           EnvironmentVariableTarget.Machine);

        // Define an array of environment variables.
        string[] envVars = { defaultEnvVar,processEnvVar, userEnvVar, machineEnvVar };

        // Try to get the environment variables from each target.
        // The default (no specified target).
        Console.WriteLine("Retrieving environment variables from the default target:");
        foreach (var envVar in envVars)
        {
          var value = Environment.GetEnvironmentVariable(envVar) ?? "(none)";
          Console.WriteLine($"   {envVar}: {value}");
        }
        // The process block.
        Console.WriteLine("\nRetrieving environment variables from the Process target:");
        foreach (var envVar in envVars)
        {
          var value = Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.Process) ?? "(none)";
          Console.WriteLine($"   {envVar}: {value}");
        }
        // The user block.
        Console.WriteLine("\nRetrieving environment variables from the User target:");
        foreach (var envVar in envVars)
        {
          var value = Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.User) ?? "(none)";
          Console.WriteLine($"   {envVar}: {value}");
        }
        // The machine block.
        Console.WriteLine("\nRetrieving environment variables from the Machine target:");
        foreach (var envVar in envVars)
        {
          var value = Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.Machine) ?? "(none)";
          Console.WriteLine($"   {envVar}: {value}");
        }

        // Delete the environment variable for each target.
        Console.WriteLine("\nDeleting environment variables for each target...\n");
        // The default target (the current process).
        Environment.SetEnvironmentVariable(defaultEnvVar, null);
        // The current process.
        Environment.SetEnvironmentVariable(processEnvVar, null,
                                           EnvironmentVariableTarget.Process);
        // The current user.
        Environment.SetEnvironmentVariable(userEnvVar, null,
                                           EnvironmentVariableTarget.User);
        // The local machine.
        Environment.SetEnvironmentVariable(machineEnvVar, null,
                                           EnvironmentVariableTarget.Machine);
    }
}
// The example displays the following output if run on a Windows system:
//      Setting environment variables for each target...
//
//      Retrieving environment variables from the default target:
//        defaultEnvVar: dft
//        processEnvVar: process
//        userEnvVar: user
//        machineEnvVar: (none)
//
//      Retrieving environment variables from the Process target:
//        defaultEnvVar: dft
//        processEnvVar: process
//        userEnvVar: user
//        machineEnvVar: (none)
//
//      Retrieving environment variables from the User target:
//        defaultEnvVar: (none)
//        processEnvVar: (none)
//        userEnvVar: user
//        machineEnvVar: (none)
//
//      Retrieving environment variables from the Machine target:
//        defaultEnvVar: (none)
//        processEnvVar: (none)
//        userEnvVar: (none)
//        machineEnvVar: machine
//
//      Deleting environment variables for each target...
//
// The example displays the following output if run on a Unix-based system:
//
//      Setting environment variables for each target...
//
//      Retrieving environment variables from the default target:
//        defaultEnvVar: dft
//        processEnvVar: process
//        userEnvVar: (none)
//        machineEnvVar: (none)
//
//      Retrieving environment variables from the Process target:
//        defaultEnvVar: dft
//        processEnvVar: process
//        userEnvVar: (none)
//        machineEnvVar: (none)
//
//      Retrieving environment variables from the User target:
//        defaultEnvVar: (none)
//        processEnvVar: (none)
//        userEnvVar: (none)
//        machineEnvVar: (none)
//
//      Retrieving environment variables from the Machine target:
//        defaultEnvVar: (none)
//        processEnvVar: (none)
//        userEnvVar: (none)
//        machineEnvVar: (none)
//
//      Deleting environment variables for each target...

注解

有关此 API 的详细信息，请参阅 Environment.GetEnvironmentVariable 的补充 API 备注。

另请参阅

• SetEnvironmentVariable(String, String, EnvironmentVariableTarget)
• GetEnvironmentVariables()
• EnvironmentVariableTarget