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GetEnvironmentVariable() and SetEnvironmentVariable() for PATH Variable

Asked 2011-08-19T12:51:40.730
15

I want to extend the current PATH variable with a C# program. Here I have several problems:

  1. Using GetEnvironmentVariable("PATH", EnvironmentVariableTarget.Machine) replaces the placeholders (i.e. '%SystemRoot%\system32' is replaced by the current path 'C:\Windows\system32'). Updating the PATH variable, I dont want to replace the placeholder with the path.

  2. After SetEnvironmentVariable no program can't be opened from the command box anymore (i.e. calc.exe in the command box doesn't work). Im using following code:

String oldPath = Environment.GetEnvironmentVariable("PATH", EnvironmentVariableTarget.Machine);
Environment.SetEnvironmentVariable("PATH", oldPath + ";%MYDIR%", EnvironmentVariableTarget.Machine);

After editing and changing the PATH variable with Windows everything works again. (I thing changes are required, otherwise it is not overwritten)

c# .net windows environment-variables
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1 Answer

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Using Registry.GetValue will expand the placeholders, so I recommend using Registry.LocalMachine.OpenSubKey, then get the value from the sub key with options set to not expand environment variables. Once you've manipulated the path to your liking, use the registry to set the value again. This will prevent Windows "forgetting" your path as you mentioned in the second part of your question.

const string pathKeyName = @"SYSTEM\CurrentControlSet\Control\Session Manager\Environment";
var pathKey = Registry.LocalMachine.OpenSubKey(pathKeyName);
var path = (string)pathKey.GetValue("PATH", "", RegistryValueOptions.DoNotExpandEnvironmentNames);
// Manipulate path here, storing in path
Registry.SetValue(String.Concat(@"HKEY_LOCAL_MACHINE\", pathKeyName), "PATH", path);
answered 2012-04-17T17:09:10.167

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