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EnvironmentVariableTarget Enumeration

Specifies the location where an environment variable is stored or retrieved in a set or get operation.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

[ComVisibleAttribute(true)]
public enum EnvironmentVariableTarget

Member nameDescription
ProcessThe environment variable is stored or retrieved from the environment block associated with the current process.

The user creates the environment variable in a set operation.

When the process terminates, the operating system destroys the environment variable in that process.

UserThe environment variable is stored or retrieved from the HKEY_CURRENT_USER\Environment key in the Windows operating system registry.

When the user creates the environment variable in a set operation, the operating system stores the environment variable in the system registry, but not in the current process. If the user starts a new process, the operating system copies the environment variable from the registry to that process.

When the process terminates, the operating system destroys the environment variable in that process. However, the environment variable in the registry persists until the user removes it programmatically or by means of an operating system tool.

MachineThe environment variable is stored or retrieved from the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment key in the Windows operating system registry.

When a user creates the environment variable in a set operation, the operating system stores the environment variable in the system registry, but not in the current process. If any user on the local machine starts a new process, the operating system copies the environment variable from the registry to that process.

When the process terminates, the operating system destroys the environment variable in that process. However, the environment variable in the registry persists until a user removes it programmatically or by means of an operating system tool.

The EnvironmentVariableTarget enumeration is used by certain overloads of the SetEnvironmentVariable, GetEnvironmentVariable, and GetEnvironmentVariables methods to specify the location, or target, where the name and value of an environment variable is stored or retrieved.

The target can be one of three locations: the environment block associated with the current process, the Windows operating system registry key reserved for environment variables associated with the current user, or the registry key reserved for environment variables associated with all users on the local machine.

The following code example demonstrates the EnvironmentVariableTarget enumeration in methods that create, modify, and delete environment variables.

// This example demonstrates the  
//     Environment.GetEnvironmentVariable, 
//     Environment.SetEnvironmentVariable, and  
//     Environment.GetEnvironmentVariables overloaded methods. 

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

class Sample 
{
//------------------------------------------------------------------------------------- 
// Globals:  
//------------------------------------------------------------------------------------- 
    protected static string fmtNameValue = "  {0} {1}.";
    protected static string myVarSuffix = "_GETSET_ENVAR_SAMPLE";

// Four relatively unique environment variable names. 
    protected static string myVarA = "A" + myVarSuffix; // default process 
    protected static string myVarB = "B" + myVarSuffix; // Current Process 
    protected static string myVarC = "C" + myVarSuffix; // Current User 
    protected static string myVarD = "D" + myVarSuffix; // Local Machine 
//===================================================================================== 
// EachVariable:  
// Test whether a specific environment variable exists in a target. 
// This section demonstrates Environment.GetEnvironmentVariable. 
//------------------------------------------------------------------------------------- 
    protected static void EachVariable(string var, EnvironmentVariableTarget tgt)
    {
    string str;
    // 
    if (0 == tgt)          // Zero means use the default target.
        str = Environment.GetEnvironmentVariable(var);
    else
        str = Environment.GetEnvironmentVariable(var, tgt);
    Console.WriteLine(fmtNameValue, 
                      var, (String.IsNullOrEmpty(str) ? "doesn't exist" : str));
    }
//------------------------------------------------------------------------------------- 
// CheckEachVariable:  
// Uses EachVariable to test whether each environment variable exists in a target. 
//------------------------------------------------------------------------------------- 
    protected static void CheckEachVariable()
    {
    Console.WriteLine("Process:");
    EachVariable(myVarA, 0);  // Check the default target (current process)
    EachVariable(myVarB, EnvironmentVariableTarget.Process);
    EachVariable(myVarC, EnvironmentVariableTarget.Process);
    EachVariable(myVarD, EnvironmentVariableTarget.Process);
    Console.WriteLine();

    Console.WriteLine("User:");
    EachVariable(myVarA, EnvironmentVariableTarget.User);
    EachVariable(myVarB, EnvironmentVariableTarget.User);
    EachVariable(myVarC, EnvironmentVariableTarget.User);
    EachVariable(myVarD, EnvironmentVariableTarget.User);
    Console.WriteLine();

    Console.WriteLine("Machine:");
    EachVariable(myVarA, EnvironmentVariableTarget.Machine);
    EachVariable(myVarB, EnvironmentVariableTarget.Machine);
    EachVariable(myVarC, EnvironmentVariableTarget.Machine);
    EachVariable(myVarD, EnvironmentVariableTarget.Machine);
    Console.WriteLine();
    }
//===================================================================================== 
// AllVariables: CheckAllVariables helper function. 
// This section demonstrates Environment.GetEnvironmentVariables. 
//------------------------------------------------------------------------------------- 
    private static void AllVariables(EnvironmentVariableTarget tgt)
    {
    string value;
    string key;

    foreach(DictionaryEntry de in Environment.GetEnvironmentVariables(tgt))
        {
        key   = (string)de.Key;
        value = (string)de.Value;
        if (key.Contains(myVarSuffix))
            Console.WriteLine(fmtNameValue, key, value);
        }
    Console.WriteLine();
    }
//===================================================================================== 
// CheckAllVariables:  
// Uses AllVariables to test whether each environment variable exists in a target. 
//------------------------------------------------------------------------------------- 
    protected static void CheckAllVariables()
    {
    Console.WriteLine("Process:");
    AllVariables(EnvironmentVariableTarget.Process);

    Console.WriteLine("User:");
    AllVariables(EnvironmentVariableTarget.User);

    Console.WriteLine("Machine:");
    AllVariables(EnvironmentVariableTarget.Machine);
    }
//===================================================================================== 
// ChkReg: CheckRegistry helper function. 
// This function filters out irrelevant environment variables.  
//------------------------------------------------------------------------------------- 
    private static void ChkReg(RegistryKey rk)
    {
    bool exists = false;
    string registryNone = "  Environment variable doesn't exist.";

    foreach (string s in rk.GetValueNames())
        {
        if (s.Contains(myVarSuffix))
            {
            Console.WriteLine(fmtNameValue, s, (string)rk.GetValue(s));
            exists = true;
            }
        }
    if (exists == false)
        Console.WriteLine(registryNone);
    Console.WriteLine();
    }
//------------------------------------------------------------------------------------- 
// CheckRegistry:  
// Uses ChkReg to display the User and Machine environment variables in the registry. 
//------------------------------------------------------------------------------------- 
    protected static void CheckRegistry()
    {
    string subkeyU = @"Environment";
    string subkeyM = @"System\CurrentControlSet\Control\Session Manager\Environment";
    string fmtSubkey = "\"{0}\" key:";

    Console.WriteLine(fmtSubkey, subkeyU);
    ChkReg(Registry.CurrentUser.OpenSubKey(subkeyU));

    Console.WriteLine(fmtSubkey, subkeyM);
    ChkReg(Registry.LocalMachine.OpenSubKey(subkeyM));
    }
//===================================================================================== 
// Main: 
//------------------------------------------------------------------------------------- 
    public static void Main() 
    {
//------------------------------------------------------------------------------------- 
// Environment variable values 
//-------------------------------------------------------------------------------------
    string existsA = "exists in the default target (Process)";
    string existsB = "exists in Process";
    string existsC = "exists in User";
    string existsD = "exists in Machine";
//------------------------------------------------------------------------------------- 
// Messages: 
//-------------------------------------------------------------------------------------
    string msg1  = "Step 1:\n" +
                       "  Check whether the environment variables already exist in \n" + 
                       "  the various targets...\n";
    string msg2  = "Step 2:\n" +
                       "  Set the environment variable for each target...\n";
    string msg31 = "Step 3, part 1:\n" + 
                       "  Display the environment variables in each target...\n";
    string msg32 = "Step 3, part 2:\n" +
                       "  Check whether the User and Machine environment variables \n" +
                       "  were created in the Windows operating system registry...\n";
    string msg41 = "Step 4, part 1:\n" +
                       "  Delete the environment variables created for this sample...\n";
    string msg42 = "Step 4, part 2:\n" +
                       "  Check whether the environment variables were deleted \n" +
                       "  in each target...\n";
    string msg43 = "Step 4, part 3:\n" + 
                       "  Check whether the User and Machine environment variables \n" +
                       "  were deleted from the Windows operating system registry...\n";
    string fmt2x   = "  {0,9}: Set {1} = \"{2}\"";
//------------------------------------------------------------------------------------- 
// Step 1: 
// Check whether the sample environment variables already exist. 
// WARNING: These variables will be deleted at the end of this sample. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg1);
    CheckEachVariable();
    Console.WriteLine();
//------------------------------------------------------------------------------------- 
// Step 2: 
// Set the environment variable for each target. 
// This section demonstrates Environment.SetEnvironmentVariable. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg2);
// Set the environment variable for the default target (the current process).
    Console.WriteLine(fmt2x, "(default)", myVarA, existsA);
    Environment.SetEnvironmentVariable(myVarA, existsA);

// Set the environment variable for the the current process.
    Console.WriteLine(fmt2x, "Process", myVarB, existsB);
    Environment.SetEnvironmentVariable(myVarB, existsB, 
        EnvironmentVariableTarget.Process);

// Set the environment variable for the the current user.
    Console.WriteLine(fmt2x, "User", myVarC, existsC);
    Environment.SetEnvironmentVariable(myVarC, existsC, 
        EnvironmentVariableTarget.User);

// Set the environment variable for the the local machine.
    Console.WriteLine(fmt2x, "Machine", myVarD, existsD);
    Environment.SetEnvironmentVariable(myVarD, existsD, 
        EnvironmentVariableTarget.Machine);
    Console.WriteLine();
//------------------------------------------------------------------------------------- 
// Step 3, part 1: 
// Display the environment variables in each target. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg31);
    CheckAllVariables();
    Console.WriteLine();
//------------------------------------------------------------------------------------- 
// Step 3, part 2: 
// Check whether the User and Machine environment variables were created in the Windows  
// operating system registry. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg32);
    CheckRegistry();
    Console.WriteLine();
//------------------------------------------------------------------------------------- 
// Step 4, part 1: 
// Delete the environment variables created for this sample. 
// This section demonstrates using Environment.SetEnvironmentVariable to delete an  
// environment variable. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg41);
    Environment.SetEnvironmentVariable(myVarA, null);
    Environment.SetEnvironmentVariable(myVarB, null, EnvironmentVariableTarget.Process);
    Environment.SetEnvironmentVariable(myVarC, null, EnvironmentVariableTarget.User);
    Environment.SetEnvironmentVariable(myVarD, null, EnvironmentVariableTarget.Machine);
//------------------------------------------------------------------------------------- 
// Step 4, part 2: 
// Check whether the environment variables were deleted in each target. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg42);
    CheckEachVariable();
//------------------------------------------------------------------------------------- 
// Step 4, part 3: 
// Check whether the User and Machine environment variables were deleted from the  
// Windows operating system registry. 
//-------------------------------------------------------------------------------------
    Console.WriteLine(msg43);
    CheckRegistry();
    }
}
/*
This example produces the following results:

Step 1:
  Check whether the environment variables already exist in
  the various targets...

Process:
  A_GETSET_ENVAR_SAMPLE doesn't exist.
  B_GETSET_ENVAR_SAMPLE doesn't exist.
  C_GETSET_ENVAR_SAMPLE doesn't exist.
  D_GETSET_ENVAR_SAMPLE doesn't exist.

User:
  A_GETSET_ENVAR_SAMPLE doesn't exist.
  B_GETSET_ENVAR_SAMPLE doesn't exist.
  C_GETSET_ENVAR_SAMPLE doesn't exist.
  D_GETSET_ENVAR_SAMPLE doesn't exist.

Machine:
  A_GETSET_ENVAR_SAMPLE doesn't exist.
  B_GETSET_ENVAR_SAMPLE doesn't exist.
  C_GETSET_ENVAR_SAMPLE doesn't exist.
  D_GETSET_ENVAR_SAMPLE doesn't exist.


Step 2:
  Set the environment variable for each target...

  (default): Set A_GETSET_ENVAR_SAMPLE = "exists in the default target (Process)"
    Process: Set B_GETSET_ENVAR_SAMPLE = "exists in Process"
       User: Set C_GETSET_ENVAR_SAMPLE = "exists in User"
    Machine: Set D_GETSET_ENVAR_SAMPLE = "exists in Machine"

Step 3, part 1:
  Display the environment variables in each target...

Process:
  B_GETSET_ENVAR_SAMPLE exists in Process.
  A_GETSET_ENVAR_SAMPLE exists in the default target (Process).

User:
  C_GETSET_ENVAR_SAMPLE exists in User.

Machine:
  D_GETSET_ENVAR_SAMPLE exists in Machine.


Step 3, part 2:
  Check whether the User and Machine environment variables
  were created in the Windows operating system registry...

"Environment" key:
  C_GETSET_ENVAR_SAMPLE exists in User.

"System\CurrentControlSet\Control\Session Manager\Environment" key:
  D_GETSET_ENVAR_SAMPLE exists in Machine.


Step 4, part 1:
  Delete the environment variables created for this sample...

Step 4, part 2:
  Check whether the environment variables were deleted
  in each target...

Process:
  A_GETSET_ENVAR_SAMPLE doesn't exist.
  B_GETSET_ENVAR_SAMPLE doesn't exist.
  C_GETSET_ENVAR_SAMPLE doesn't exist.
  D_GETSET_ENVAR_SAMPLE doesn't exist.

User:
  A_GETSET_ENVAR_SAMPLE doesn't exist.
  B_GETSET_ENVAR_SAMPLE doesn't exist.
  C_GETSET_ENVAR_SAMPLE doesn't exist.
  D_GETSET_ENVAR_SAMPLE doesn't exist.

Machine:
  A_GETSET_ENVAR_SAMPLE doesn't exist.
  B_GETSET_ENVAR_SAMPLE doesn't exist.
  C_GETSET_ENVAR_SAMPLE doesn't exist.
  D_GETSET_ENVAR_SAMPLE doesn't exist.

Step 4, part 3:
  Check whether the User and Machine environment variables
  were deleted from the Windows operating system registry...

"Environment" key:
  Environment variable doesn't exist.

"System\CurrentControlSet\Control\Session Manager\Environment" key:
  Environment variable doesn't exist.
*/

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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