Environment.SetEnvironmentVariable 方法

參考

定義

命名空間:: System

組件:: System.Runtime.Extensions.dll

組件:: System.Runtime.dll

組件:: mscorlib.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

建立、修改或刪除環境變數。

多載

SetEnvironmentVariable(String, String)	建立、修改或刪除儲存在目前進程中的環境變數。
SetEnvironmentVariable(String, String, EnvironmentVariableTarget)	建立、修改或刪除儲存在目前進程或保留給目前使用者或本機計算機的 Windows 作業系統登錄機碼中的環境變數。

SetEnvironmentVariable(String, String)

來源:: Environment.cs

來源:: Environment.cs

來源:: Environment.cs

建立、修改或刪除儲存在目前進程中的環境變數。

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)

參數

variable: String

環境變數的名稱。

value: String

要指派給 variable的值。

例外狀況

ArgumentNullException

variable null。

ArgumentException

variable 包含長度為零的字串、初始十六進位零字元（0x00），或等號（“=” ）。

-或-

variable 或 value 長度大於或等於 32,767 個字元。

-或-

執行此作業期間發生錯誤。

SecurityException

呼叫端沒有執行這項作業的必要許可權。

範例

下列範例會嘗試從進程環境區塊擷取名為 Test1 的環境變數值。如果變數不存在，此範例會建立變數並擷取其值。此範例會顯示變數的值。針對在 Windows 系統上執行的 .NET 實作，它也會使用 EnvironmentVariableTarget 列舉的每個成員呼叫 GetEnvironmentVariables(EnvironmentVariableTarget) 方法，以建立變數只能從目前的進程環境區塊擷取。（類似 Unix 系統上的 .NET 實作僅支援進程環境區塊中的變數。最後，如果範例建立變數，則會將其刪除。

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.

備註

呼叫這個方法相當於呼叫具有 target 自變數 EnvironmentVariableTarget.Process 值的 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 多載。

在類似 Unix 的系統上，對 SetEnvironmentVariable(String, String) 方法的呼叫不會影響任何原生連結庫，或將會載入。（相反地，由原生連結庫所進行的進程環境修改，不會由Managed呼叫端看到。

如果 value 自變數未 null，且 variable 參數所命名的環境變數不存在，則會建立環境變數並指派 value的內容。如果存在，則會修改其值。因為環境變數只定義於目前進程的環境區塊中，所以不會在進程結束之後保存。

如果 variable 包含非初始十六進位零字元，則零字元之前的字元會被視為環境變數名稱，並忽略所有後續字元。

如果 value 包含非初始十六進位零字元，則會將零字元指派給環境變數之前的字元，並忽略所有後續字元。

如果 valuenull 或 .NET 9 之前的版本中是空的，且 variable 所命名的環境變數存在，則會刪除環境變數。如果 variable 不存在，即使無法執行作業，也不會發生任何錯誤。在下列任何情況下，value 視為空白：

String.Empty。
它包含單一字元，其值為U+0000。

另請參閱

適用於

SetEnvironmentVariable(String, String, EnvironmentVariableTarget)

來源:: Environment.cs

來源:: Environment.cs

來源:: Environment.cs

建立、修改或刪除儲存在目前進程或保留給目前使用者或本機計算機的 Windows 作業系統登錄機碼中的環境變數。

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)

參數

variable: String

環境變數的名稱。

value: String

要指派給 variable的值。

target: EnvironmentVariableTarget

其中一個列舉值，指定環境變數的位置。

例外狀況

ArgumentNullException

variable null。

ArgumentException

variable 包含長度為零的字串、初始十六進位零字元（0x00），或等號（“=” ）。

-或-

variable 長度大於或等於 32,767 個字元。

-或-

target 不是 EnvironmentVariableTarget 列舉的成員。

-或-

target 是 Machine 或 User，且 variable 長度大於或等於 255。

-或-

target 是 Process，且 value 長度大於或等於 32,767 個字元。

-或-

執行此作業期間發生錯誤。

SecurityException

呼叫端沒有執行這項作業的必要許可權。

範例

下列範例會建立 EnvironmentVariableTarget.Process、EnvironmentVariableTarget.User和 Machine 目標的環境變數，檢查操作系統登錄是否包含使用者和計算機環境變數，然後刪除環境變數。由於類似 Unix 系統上的 .NET 不支援每個使用者和每部電腦的環境變數，因此只有 SetEnvironmentVariable(String, String) 和 SetEnvironmentVariable(String, String, EnvironmentVariableTarget)，且值為 EnvironmentVariableTarget.Process 成功將環境變數儲存至進程環境區塊。

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...

備註

SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 方法可讓您定義目前進程可用的環境變數（Process 值）。目前進程環境區塊唯一的環境變數只會持續到進程結束為止。

此外，在僅限 Windows 系統上，SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 方法可讓您定義環境變數，可供計算機上執行的所有進程使用（EnvironmentVariableTarget.Machine 值），以及使用者執行的所有進程（EnvironmentVariableTarget.User 值）。每部計算機和每個用戶環境變數會複製到目前進程的環境區塊中。

在類似 Unix 的系統上，會忽略具有 EnvironmentVariableTarget.Machine 或 EnvironmentVariableTarget.User 值的 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 方法呼叫。

在類似 Unix 的系統上，呼叫值為 EnvironmentVariableTarget.Process 的 SetEnvironmentVariable(String, String, EnvironmentVariableTarget) 方法，不會影響任何原生連結庫，或將會載入。（相反地，由原生連結庫所進行的進程環境修改，不會由Managed呼叫端看到。

如果 value 自變數未 null，且 variable 自變數所命名的環境變數不存在，則會建立環境變數並指派 value的內容。如果存在，則會修改其值。

如果 variable 包含非初始十六進位零字元，則零字元之前的字元會被視為環境變數名稱，並忽略所有後續字元。

如果 value 包含非初始十六進位零字元，則會將零字元指派給環境變數之前的字元，並忽略所有後續字元。

如果 valuenull 或 .NET 9 之前的版本中是空的，且 variable 所命名的環境變數存在，則會刪除環境變數。在下列任何情況下，value 視為空白：

String.Empty。
它包含單一字元，其值為U+0000。

如果 variable 不存在，雖然無法執行作業，但不會發生任何錯誤。當 targetMachine時請小心，因為您不小心刪除會影響整個本機計算機的環境變數，而不只是目前的進程或使用者。

Windows 系統上的 EnvironmentVariableTarget.Machine 和 EnvironmentVariableTarget.User

如果 target 是 EnvironmentVariableTarget.User，則環境變數會儲存在本機計算機登錄的 HKEY_CURRENT_USER\Environment 機碼中。它也會複製到以目前使用者身分執行的檔案總管實例。然後，使用者從檔案總管啟動的任何新進程都會繼承環境變數。

同樣地，如果 target 是 EnvironmentVariableTarget.Machine，則環境變數會儲存在本機計算機登錄的 HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager\Environment 機碼中。它也會複製到檔案總管的所有實例。環境變數接著會由從 [檔案總管] 啟動的任何新進程繼承。

如果 target 是 User 或 Machine，則 Windows WM_SETTINGCHANGE 訊息會通知設定作業的其他應用程式。

如果 target 是 EnvironmentVariableTarget.User 或 EnvironmentVariableTarget.Machine，建議長度 value 小於 2048 個字元。

另請參閱

適用於

共用方式為

Environment.SetEnvironmentVariable 方法

定義

多載

SetEnvironmentVariable(String, String)

參數

例外狀況

範例

備註

另請參閱

適用於

SetEnvironmentVariable(String, String, EnvironmentVariableTarget)

參數

例外狀況

範例

備註

Windows 系統上的 EnvironmentVariableTarget.Machine 和 EnvironmentVariableTarget.User

另請參閱

適用於

其他資源