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Environment.GetEnvironmentVariable Method (String, EnvironmentVariableTarget)

Retrieves the value of an environment variable from the current process or from the Windows operating system registry key for the current user or local machine.

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

'Declaration
Public Shared Function GetEnvironmentVariable ( _
	variable As String, _
	target As EnvironmentVariableTarget _
) As String

Parameters

variable
Type: System.String
The name of an environment variable.
target
Type: System.EnvironmentVariableTarget
One of the EnvironmentVariableTarget values.

Return Value

Type: System.String
The value of the environment variable specified by the variable and target parameters, or Nothing if the environment variable is not found.

ExceptionCondition
ArgumentNullException

variable is Nothing.

ArgumentException

target is not a valid EnvironmentVariableTarget value.

SecurityException

The caller does not have the required permission to perform this operation.

The target parameter specifies whether the environment variable is retrieved from the current process or from the Windows operating system registry key for the current user or local machine.

Environment variable names are not case-sensitive.

The following example creates environment variables for the Process, User, and Machine targets, checks whether the operating system registry contains the User and Machine environment variables, then deletes the environment variables.


' This example demonstrates the 
'     Environment.GetEnvironmentVariable,
'     Environment.SetEnvironmentVariable, and 
'     Environment.GetEnvironmentVariables overloaded methods.
Imports System
Imports System.Collections
Imports Microsoft.Win32
Imports Microsoft.VisualBasic

Class Sample
   '-------------------------------------------------------------------------------------
   ' Globals: 
   '-------------------------------------------------------------------------------------
   Protected Shared fmtNameValue As String = "  {0} {1}."
   Protected Shared myVarSuffix As String = "_GETSET_ENVAR_SAMPLE"

   ' Four relatively unique environment variable names.
   Protected Shared myVarA As String = "A" & myVarSuffix ' default process
   Protected Shared myVarB As String = "B" & myVarSuffix ' Current Process
   Protected Shared myVarC As String = "C" & myVarSuffix ' Current User
   Protected Shared myVarD As String = "D" & myVarSuffix ' Local Machine
   '=====================================================================================
   ' EachVariable: 
   ' Test whether a specific environment variable exists in a target.
   ' This section demonstrates Environment.GetEnvironmentVariable.
   '-------------------------------------------------------------------------------------
   Protected Shared Sub EachVariable(var As String, tgt As EnvironmentVariableTarget)
      Dim str As String
      '
      If 0 = tgt Then ' Zero means use the default target.
         str = Environment.GetEnvironmentVariable(var)
      Else
         str = Environment.GetEnvironmentVariable(var, tgt)
      End If
      Console.WriteLine(fmtNameValue, var, IIf(String.IsNullOrEmpty(str), _
                                              "doesn't exist", str))
   End Sub 'EachVariable

   '-------------------------------------------------------------------------------------
   ' CheckEachVariable: 
   ' Uses EachVariable to test whether each environment variable exists in a target.
   '-------------------------------------------------------------------------------------
   Protected Shared Sub 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()
   End Sub 'CheckEachVariable

   '=====================================================================================
   ' AllVariables: CheckAllVariables helper function.
   ' This section demonstrates Environment.GetEnvironmentVariables.
   '-------------------------------------------------------------------------------------
   Private Shared Sub AllVariables(tgt As EnvironmentVariableTarget)
      Dim value As String
      Dim key As String

      Dim de As DictionaryEntry
      For Each de In Environment.GetEnvironmentVariables(tgt)
         key = CStr(de.Key)
         value = CStr(de.Value)
         If key.Contains(myVarSuffix) Then
            Console.WriteLine(fmtNameValue, key, value)
         End If
      Next de
      Console.WriteLine()
   End Sub 'AllVariables

   '=====================================================================================
   ' CheckAllVariables: 
   ' Uses AllVariables to test whether each environment variable exists in a target.
   '-------------------------------------------------------------------------------------
   Protected Shared Sub CheckAllVariables()
      Console.WriteLine("Process:")
      AllVariables(EnvironmentVariableTarget.Process)

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

      Console.WriteLine("Machine:")
      AllVariables(EnvironmentVariableTarget.Machine)
   End Sub 'CheckAllVariables

   '=====================================================================================
   ' ChkReg: CheckRegistry helper function.
   ' This function filters out irrelevant environment variables. 
   '-------------------------------------------------------------------------------------
   Private Shared Sub ChkReg(rk As RegistryKey)
      Dim exists As Boolean = False
      Dim registryNone As String = "  Environment variable doesn't exist."

      Dim s As String
      For Each s In rk.GetValueNames()
         If s.Contains(myVarSuffix) Then
            Console.WriteLine(fmtNameValue, s, CStr(rk.GetValue(s)))
            exists = True
         End If
      Next s
      If exists = False Then
         Console.WriteLine(registryNone)
      End If
      Console.WriteLine()
   End Sub 'ChkReg

   '-------------------------------------------------------------------------------------
   ' CheckRegistry: 
   ' Uses ChkReg to display the User and Machine environment variables in the registry.
   '-------------------------------------------------------------------------------------
   Protected Shared Sub CheckRegistry()
      Dim subkeyU As String = "Environment"
      Dim subkeyM As String = "System\CurrentControlSet\Control\Session Manager\Environment"
      Dim fmtSubkey As String = """{0}"" key:"

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

      Console.WriteLine(fmtSubkey, subkeyM)
      ChkReg(Registry.LocalMachine.OpenSubKey(subkeyM))
   End Sub 'CheckRegistry

   '=====================================================================================
   ' Main:
   '-------------------------------------------------------------------------------------
   Public Shared Sub Main()
      '-------------------------------------------------------------------------------------
      ' Environment variable values
      '-------------------------------------------------------------------------------------
      Dim existsA As String = "exists in the default target (Process)"
      Dim existsB As String = "exists in Process"
      Dim existsC As String = "exists in User"
      Dim existsD As String = "exists in Machine"
      '-------------------------------------------------------------------------------------
      ' Messages:
      '-------------------------------------------------------------------------------------
      Dim msg1  As String = "Step 1:" & vbCrLf & _
                            "  Check whether the environment variables already exist in " _
                 & vbCrLf & "  the various targets..." & vbCrLf
      Dim msg2  As String = "Step 2:" & vbCrLf & _
                            "  Set the environment variable for each target..." & vbCrLf
      Dim msg31 As String = "Step 3, part 1:" & vbCrLf & _
                            "  Display the environment variables in each target..." & vbCrLf
      Dim msg32 As String = "Step 3, part 2:" & vbCrLf & _
                            "  Check whether the User and Machine environment variables " _
                 & vbCrLf & "  were created in the Windows operating system registry..." _
                 & vbCrLf
      Dim msg41 As String = "Step 4, part 1:" & vbCrLf & _
                            "  Delete the environment variables created for this sample..." _
                 & vbCrLf
      Dim msg42 As String = "Step 4, part 2:" & vbCrLf & _
                            "  Check whether the environment variables were deleted " _
                 & vbCrLf & "  in each target..." & vbCrLf
      Dim msg43 As String = "Step 4, part 3:" & vbCrLf & _
                            "  Check whether the User and Machine environment variables " _
                 & vbCrLf & "  were deleted from the Windows operating system registry..." _
                 & vbCrLf
      Dim fmt2x As String = "  {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, Nothing)
      Environment.SetEnvironmentVariable(myVarB, Nothing, EnvironmentVariableTarget.Process)
      Environment.SetEnvironmentVariable(myVarC, Nothing, EnvironmentVariableTarget.User)
      Environment.SetEnvironmentVariable(myVarD, Nothing, 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()
   End Sub 'Main
End Class 'Sample
'
'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.
'


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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