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Environment.ExpandEnvironmentVariables Method

Replaces the name of each environment variable embedded in the specified string with the string equivalent of the value of the variable, then returns the resulting string.

[Visual Basic]
Public Shared Function ExpandEnvironmentVariables( _
   ByVal name As String _
) As String
[C#]
public static string ExpandEnvironmentVariables(
 string name
);
[C++]
public: static String* ExpandEnvironmentVariables(
 String* name
);
[JScript]
public static function ExpandEnvironmentVariables(
   name : String
) : String;

Parameters

name
A string containing the names of zero or more environment variables. Each environment variable is quoted with the percent sign character (%).

Return Value

A string with each environment variable replaced by its value.

Exceptions

Exception Type Condition
ArgumentNullException name is a null reference (Nothing in Visual Basic).

Remarks

COM interop is used to retrieve the environment variables from the operating system. If the environment variables cannot be retrieved due to a COM error, the HRESULT that explains the cause of the failure is used to generate one of several possible exceptions; that is, the exception depends on the HRESULT. For more information about how the HRESULT is processed, see the Remarks section of the Marshal.ThrowExceptionForHR method.

Replacement only occurs for environment variables that are set. For example, suppose name is "MyENV = %MyENV%". If the environment variable, MyENV, is set to 42, this method returns "MyENV = 42". If MyENV is not set, no change occurs; this method returns "MyENV = %MyENV%".

The size of the return value is limited to 32K on Windows NT 4.0 and earlier, and Windows 2000 and later. There is no size restriction on Windows 98 and Windows Me.

Example

[Visual Basic] 
' Sample for the Environment.ExpandEnvironmentVariables method
Imports System

Class Sample
   Public Shared Sub Main()
      Dim str As [String]
      Dim nl As [String] = Environment.NewLine
      
      Console.WriteLine()
      '  <-- Keep this information secure! -->
      Dim query As [String] = "My system drive is %SystemDrive% and" & _ 
                              "my system root is %SystemRoot%"
      str = Environment.ExpandEnvironmentVariables(query)
      Console.WriteLine("ExpandEnvironmentVariables: {0}  {1}", nl, str)
   End Sub 'Main
End Class 'Sample
'
'This example produces the following results:
'
'ExpandEnvironmentVariables:
'  My system drive is C: and my system root is C:\WINNT
'

[C#] 
// Sample for the Environment.ExpandEnvironmentVariables method
using System;

class Sample 
{
    public static void Main() 
    {
    String str;
    String nl = Environment.NewLine;

    Console.WriteLine();
//  <-- Keep this information secure! -->
    String query = "My system drive is %SystemDrive% and my system root is %SystemRoot%";
    str = Environment.ExpandEnvironmentVariables(query);
    Console.WriteLine("ExpandEnvironmentVariables: {0}  {1}", nl, str);
    }
}
/*
This example produces the following results:

ExpandEnvironmentVariables:
  My system drive is C: and my system root is C:\WINNT
*/

[C++] 
// Sample for the Environment::ExpandEnvironmentVariables method
#using <mscorlib.dll>

using namespace System;

int main() {
   String* str;
   String*  nl = Environment::NewLine;

   Console::WriteLine();
   //  <-- Keep this information secure! -->
   String*  query = S"My system drive is %SystemDrive% and my system root is %SystemRoot%";
   str = Environment::ExpandEnvironmentVariables(query);
   Console::WriteLine(S"ExpandEnvironmentVariables: {0} {1}", nl, str);
}
/*
This example produces the following results:

ExpandEnvironmentVariables:
My system drive is C: and my system root is C:\WINNT
*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

.NET Framework Security: 

See Also

Environment Class | Environment Members | System Namespace

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