Environment.SetEnvironmentVariable 方法

参考

定义

命名空间:: System

程序集:: System.Runtime.Extensions.dll

程序集:: System.Runtime.dll

程序集:: mscorlib.dll

程序集:: netstandard.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

创建、修改或删除环境变量。

重载

SetEnvironmentVariable(String, String)	创建、修改或删除当前进程中存储的环境变量。
SetEnvironmentVariable(String, String, EnvironmentVariableTarget)	创建、修改或删除当前进程中或者为当前用户或本地计算机保留的 Windows 操作系统注册表项中存储的环境变量。

SetEnvironmentVariable(String, String)

创建、修改或删除当前进程中存储的环境变量。

public:
 static void SetEnvironmentVariable(System::String ^ variable, System::String ^ value);

public static void SetEnvironmentVariable (string variable, string value);

public static void SetEnvironmentVariable (string variable, string? value);

static member SetEnvironmentVariable : string * string -> unit

Public Shared Sub SetEnvironmentVariable (variable As String, value As String)

参数

variable: String

环境变量名。

value: String

要分配给 variable 的值。

例外

ArgumentNullException

variable 为 null。

ArgumentException

variable 包含一个长度为零的字符串、一个初始十六进制零字符 (0x00) 或一个等号 ("=")。

- 或 -

variable 或 value 的长度大于或等于 32,767 个字符。

- 或 -

执行此操作期间出错。

SecurityException

调用方没有执行此操作所需的权限。

示例

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，示例将创建变量并检索其值。该示例显示变量的值。对于在 Windows 系统上运行的 .NET 实现，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变量。基于 Unix 的系统上的 (.NET 实现仅支持进程环境 block 中的变量。) 最后，如果示例创建了变量，则会将其删除。

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.

module Example

open System

let mutable toDelete = false

// Check whether the environment variable exists.
let value = 
    let v = Environment.GetEnvironmentVariable "Test1"
    // If necessary, create it.
    if isNull v then
        Environment.SetEnvironmentVariable("Test1", "Value1")
        toDelete <- true
        Environment.GetEnvironmentVariable "Test1"
    else 
        v

// Display the value.
printfn $"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 then
    printfn "Attempting to retrieve Test1 from:"
    for enumValue in Enum.GetValues typeof<EnvironmentVariableTarget> do
        let value = Environment.GetEnvironmentVariable("Test1", enumValue :?> EnvironmentVariableTarget)
        printfn $"""   {enumValue}: {if value <> null then "found" else "not found"}"""
    printfn ""

// If we've created it, now delete it.
if toDelete then
    Environment.SetEnvironmentVariable("Test1", null)
    // Confirm the deletion.
    if Environment.GetEnvironmentVariable "Test1" |> isNull then
        printfn "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.

Module Example
   Public Sub Main()
      Dim value As String 
      Dim toDelete As Boolean = False
      
      ' Check whether the environment variable exists.
      value = Environment.GetEnvironmentVariable("Test1")
      ' If necessary, create it.
      If value Is Nothing Then
         Environment.SetEnvironmentVariable("Test1", "Value1")
         toDelete = True
         
         ' Now retrieve it.
         value = Environment.GetEnvironmentVariable("Test1")
      End If
      ' Display the value.
      Console.WriteLine($"Test1: {value}")
      Console.WriteLine()
      
      ' 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 Then
         Console.WriteLine("Attempting to retrieve Test1 from:")
         For Each enumValue As EnvironmentVariableTarget In 
                           [Enum].GetValues(GetType(EnvironmentVariableTarget))
            value = Environment.GetEnvironmentVariable("Test1", enumValue)
            Console.WriteLine($"   {enumValue}: {If(value IsNot Nothing, "found", "not found")}")
         Next
         Console.WriteLine()
      End If

      ' If we've created it, now delete it.
      If toDelete Then 
         Environment.SetEnvironmentVariable("Test1", Nothing)
         ' Confirm the deletion.
         If Environment.GetEnvironmentVariable("Test1") = Nothing Then
            Console.WriteLine("Test1 has been deleted.")
         End If
      End If         
   End Sub
End Module
' 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

调用此方法等效于为参数调用 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 值为 EnvironmentVariableTarget.Process 的 target 重载。

在非 Windows 系统上，对方法的 SetEnvironmentVariable(String, String) 调用不会影响已加载或将要加载的任何本机库。

value如果参数不为空 (请参阅本节后面有关删除环境变量的讨论，了解空值的定义) 且参数variable命名的环境变量不存在，则会创建环境变量并为其分配内容value。如果确实存在，则修改其值。由于环境变量仅在当前进程的环境块中定义，因此它在进程结束后不会保留。

如果 variable 包含非初始十六进制零字符，则将零字符之前的字符视为环境变量名称，并忽略所有后续字符。

如果 value 包含非初始十六进制零字符，则将零字符之前的字符分配给环境变量，并忽略所有后续字符。

如果 value 为空且名为的 variable 环境变量存在，则删除该环境变量。如果 variable 不存在，即使无法执行该操作，也不会发生错误。 value 在以下任一条件下被视为空：

它是 null。
它是 String.Empty。
它由值为 U+0000 的单个字符组成。

另请参阅

适用于

SetEnvironmentVariable(String, String, EnvironmentVariableTarget)

创建、修改或删除当前进程中或者为当前用户或本地计算机保留的 Windows 操作系统注册表项中存储的环境变量。

public:
 static void SetEnvironmentVariable(System::String ^ variable, System::String ^ value, EnvironmentVariableTarget target);

public static void SetEnvironmentVariable (string variable, string? value, EnvironmentVariableTarget target);

public static void SetEnvironmentVariable (string variable, string value, EnvironmentVariableTarget target);

static member SetEnvironmentVariable : string * string * EnvironmentVariableTarget -> unit

Public Shared Sub SetEnvironmentVariable (variable As String, value As String, target As EnvironmentVariableTarget)

参数

variable: String

环境变量名。

value: String

要分配给 variable 的值。

target: EnvironmentVariableTarget

一个用于指定环境变量的位置的枚举值。

例外

ArgumentNullException

variable 为 null。

ArgumentException

variable 包含一个长度为零的字符串、一个初始十六进制零字符 (0x00) 或一个等号 ("=")。

- 或 -

variable 的长度大于或等于 32,767 个字符。

- 或 -

target 不是 EnvironmentVariableTarget 枚举的一个成员。

- 或 -

target 为 Machine 或 User，且 variable 的长度大于或等于 255。

- 或 -

target 为 Process ，且 value 的长度大于或等于 32767 个字符。

- 或 -

执行此操作期间出错。

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。由于基于 Unix 的系统上的 .NET 不支持每用户和每计算机环境变量，因此只有 SetEnvironmentVariable(String, String) 和 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 值为 EnvironmentVariableTarget.Process 时，才能成功将环境变量存储到进程环境块。

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...

module Sample

open System

// Environment variable names for default, process, user, and machine targets.
let rec defaultEnvVar = nameof defaultEnvVar
let rec processEnvVar = nameof processEnvVar
let rec userEnvVar = nameof userEnvVar
let rec machineEnvVar = nameof machineEnvVar

let rec dft = nameof dft
let rec proc = nameof proc
let rec user = nameof user
let rec machine = nameof machine

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

// Define a list of environment variables.
let envVars = [ defaultEnvVar; processEnvVar; userEnvVar; machineEnvVar ]

// Try to get the environment variables from each target.
// The default (no specified target).
printfn "Retrieving environment variables from the default target:"
for envVar in envVars do
    let value = 
        match Environment.GetEnvironmentVariable envVar with
        | null -> "(none)"
        | v -> v
    printfn $"   {envVar}: {value}"

// The process block.
printfn "\nRetrieving environment variables from the Process target:"
for envVar in envVars do
    let value = 
        match Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.Process) with
        | null -> "(none)"
        | v -> v
    printfn $"   {envVar}: {value}"

// The user block.
printfn "\nRetrieving environment variables from the User target:"
for envVar in envVars do
    let value = 
        match Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.User) with
        | null -> "(none)"
        | v -> v
    printfn $"   {envVar}: {value}"

// The machine block.
printfn "\nRetrieving environment variables from the Machine target:"
for envVar in envVars do
    let value = 
        match Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.Machine) with
        | null -> "(none)"
        | v -> v
    printfn $"   {envVar}: {value}"

// Delete the environment variable for each target.
printfn "\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...

Imports System.Collections
Imports Microsoft.Win32

Module Sample 
    Public Sub Main() 
        ' Environment variable names for default, process, user, and machine targets.
        Dim defaultEnvVar As String = NameOf(defaultEnvVar)
        Dim processEnvVar As String = NameOf(processEnvVar)
        Dim userEnvVar As String = NameOf(userEnvVar)
        Dim machineEnvVar As String = NameOf(machineEnvVar)

        Dim dft As String = NameOf(dft)
        Dim process As String = NameOf(process)
        Dim user As String = NameOf(user)
        Dim machine As String = NameOf(machine)

        ' Set the environment variable for each target.
        Console.WriteLine("Setting environment variables for each target...")
        ' 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)
        Console.WriteLine()

        ' Define an array of environment variables.
        Dim envVars As String() = { 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:")
        For Each envVar in envVars
          Dim value = Environment.GetEnvironmentVariable(envVar)
          Console.WriteLine($"   {envVar}: {If(value IsNot Nothing, value, "(none)")}")
        Next
        Console.WriteLine()
        ' The process block.
        Console.WriteLine("Retrieving environment variables from the Process target:")
        For Each envVar in envVars
          Dim value = Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.Process)
          Console.WriteLine($"   {envVar}: {If(value IsNot Nothing, value, "(none)")}")
        Next
        Console.WriteLine()
        ' The user block.
        Console.WriteLine("Retrieving environment variables from the User target:")
        For Each envVar in envVars
          Dim value = Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.User)
          Console.WriteLine($"   {envVar}: {value}")
        Next
        Console.WriteLine()
        ' The machine block.
        Console.WriteLine("Retrieving environment variables from the Machine target:")
        For Each envVar in envVars
          Dim value = Environment.GetEnvironmentVariable(envVar, EnvironmentVariableTarget.Machine)
          Console.WriteLine($"   {envVar}: {value}")
        Next
        Console.WriteLine()

        ' Delete the environment variable for each target.
        Console.WriteLine("Deleting environment variables for each target...")
        ' The default target (the current process).
        Environment.SetEnvironmentVariable(defaultEnvVar, Nothing)
        ' The current process.
        Environment.SetEnvironmentVariable(processEnvVar, Nothing, 
                                           EnvironmentVariableTarget.Process)
        ' The current user.
        Environment.SetEnvironmentVariable(userEnvVar, Nothing, 
                                           EnvironmentVariableTarget.User)
        ' The local machine.
        Environment.SetEnvironmentVariable(machineEnvVar, Nothing, 
                                           EnvironmentVariableTarget.Machine)
    End Sub
End Module
' 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

使用 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 方法可以定义一个环境变量，该变量可用于当前进程 (Process 值) 。对当前进程环境块唯一的环境变量仅保留到进程结束。

此外，仅在 Windows 系统上， SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 方法允许你定义一个环境变量，该变量可用于计算机上运行的所有进程 (EnvironmentVariableTarget.Machine 值) ，以及用户 (EnvironmentVariableTarget.User 值) 运行的所有进程。每计算机和每用户环境变量将复制到当前进程的环境块中。

在非 Windows 系统上，将忽略对值为或 EnvironmentVariableTarget.User 的方法的EnvironmentVariableTarget.Machine调用SetEnvironmentVariable(String, String, EnvironmentVariableTarget)。

在非 Windows 系统上，对 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 值为的方法的 EnvironmentVariableTarget.Process 调用不会影响已加载或将要加载的任何本机库。

value如果参数不为空 (请参阅本节后面有关删除环境变量的讨论，了解空值的定义) 并且参数命名的variable环境变量不存在，则会创建环境变量并为其分配内容value。如果确实存在，则修改其值。

如果 variable 包含非初始十六进制零字符，则将零字符之前的字符视为环境变量名称，并忽略所有后续字符。

如果 value 包含非初始十六进制零字符，则将零字符之前的字符分配给环境变量，并忽略所有后续字符。

如果 value 为空且名为的 variable 环境变量存在，则删除该环境变量。 value 在以下任一条件下被视为空：

它是 null。
它是 String.Empty。
它由值为 U+0000 的单个字符组成。

如果 variable 不存在，则不会发生错误，尽管无法执行该操作。当为 Machine时target要小心，因为可能会意外删除影响整个本地计算机的环境变量，而不仅仅是当前进程或用户。

Windows 系统上的 EnvironmentVariableTarget.Machine 和 EnvironmentVariableTarget.User

如果 target 为 EnvironmentVariableTarget.User，则环境变量存储在本地计算机注册表的 HKEY_CURRENT_USER\Environment 键中。它还会复制到以当前用户身份运行的文件资源管理器实例。然后，环境变量由用户从文件资源管理器启动的任何新进程继承。

同样，如果 target 为 EnvironmentVariableTarget.Machine，则环境变量存储在本地计算机注册表的 HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager\Environment 键中。它还会复制到文件资源管理器的所有实例。然后，环境变量由从文件资源管理器启动的任何新进程继承。

如果 target 为 User 或 Machine，则会通过 Windows WM_SETTINGCHANGE 消息通知其他应用程序设置操作。

如果 target 为 EnvironmentVariableTarget.User 或 EnvironmentVariableTarget.Machine，建议的长度 value 小于 2048 个字符。

另请参阅

适用于

Environment.SetEnvironmentVariable 方法

定义

重载

SetEnvironmentVariable(String, String)

参数

例外

示例

注解

另请参阅

适用于

SetEnvironmentVariable(String, String, EnvironmentVariableTarget)

参数

例外

示例

注解

Windows 系统上的 EnvironmentVariableTarget.Machine 和 EnvironmentVariableTarget.User

另请参阅

适用于

其他资源