Question: I am creating a Visual Studio 2008 Setup Wizard for my program  

<http://support.microsoft.com/kb/307353>  

I see that it is possible to add registry entries, etc..
Is there a possibility to register windows environment variable without writing a custom action?  

And if I must write a custom action, what is the least painful way to do so?

Answer: 
> 
> ***Warning***: **`Please do not use this approach`**. It is dangerous. Use built-in MSI features for environment variable update.
> 
> 
> ***Example***: Writing straight to **`HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment`** - **`Path`** will wipe out whatever is already there. Very serious.
> 
> 
> ***Solution***: MSI features the [Environment table](https://stackoverflow.com/a/8560425/129130) to facilitate merging and updating of environment variables in a reliable fashion. Note that this table is also known to be complex enough to trigger unexpected results. Please test well. Uninstall scenarios especially.
> 
> 
> 

---

Using Visual Studio 2008, you can easily do it by setting the appropriate variable in the Windows registry:

1. In the Solution Explorer, right-click on your project (not solution), and select **View->Registry**
2. Create the registry key(folder):
	1. For a **User** variable: Right-click on **HKEY\_CURRENT\_USER**, select "**New Key**", and name it "**Environment**".
	2. For a **System** variable: Right-Click on **HKEY\_LOCAL\_MACHINE**, select "**New Key**", and name it "**SYSTEM**". Continue doing this to create the path "**HKEY\_LOCAL\_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment**" .
3. Right-click on the **Environment** key(folder), select **New->String**, and give it the name you want.
4. With the string selected, find the **Properties** window (Alt+Enter will bring it up)
5. In the Properties window, fill in the **Value** you want.

If you want the Value to reference the installation directory, you can do it like this using property variables: [TARGETDIR]SomeFile.ext (see <http://msdn.microsoft.com/en-us/library/aa370905%28v=vs.85%29.aspx> for more property variables)
The top answer explains how to do it without a custom action but those looking for a custom action can use the following code as a template:

```
 [RunInstaller(true)]
public partial class GRInstallCustomAction : System.Configuration.Install.Installer
{
    string environmentKey = @"SYSTEM\CurrentControlSet\Control\Session Manager\Environment";
    string pathUrl = "C:\\Program Files (86)\\TargetFolder";
    public GRInstallCustomAction()
    {
        InitializeComponent();
    }

    [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]
    public override void Install(IDictionary stateSaver)
    {
        base.Install(stateSaver);
    }

    [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]
    public override void Commit(IDictionary savedState)
    {
        base.Commit(savedState);

        string environmentVar = Environment.GetEnvironmentVariable("PATH");

        //get non-expanded PATH environment variable            
        string oldPath = (string)Registry.LocalMachine.CreateSubKey(environmentKey).GetValue("Path", "", RegistryValueOptions.DoNotExpandEnvironmentNames);

        var index = oldPath.IndexOf(pathUrl);
        if (index < 0)
        {
            //set the path as an an expandable string
            Registry.LocalMachine.CreateSubKey(environmentKey).SetValue("Path", oldPath + ";" + pathUrl, RegistryValueKind.ExpandString);
        }

    }

    [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]
    public override void Rollback(IDictionary savedState)
    {
        base.Rollback(savedState);

    }

    [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]
    public override void Uninstall(IDictionary savedState)
    {
        base.Uninstall(savedState);

        //get non-expanded PATH environment variable            
        string oldPath = (string)Registry.LocalMachine.CreateSubKey(environmentKey).GetValue("Path", "", RegistryValueOptions.DoNotExpandEnvironmentNames);

        string removeString = pathUrl + ";";
        var index = oldPath.IndexOf(removeString);
        if (index < 0)
        {
            removeString = pathUrl;
            index = oldPath.IndexOf(removeString);
        }

        if (index > -1)
        {
            oldPath = oldPath.Remove(index, pathUrl.Length);
            //set the path as an an expandable string
            Registry.LocalMachine.CreateSubKey(environmentKey).SetValue("Path", oldPath, RegistryValueKind.ExpandString);
        }
    }
}

```

This walk-through shows you how to create and apply the custom action:
<https://msdn.microsoft.com/en-us/library/d9k65z2d(v=vs.100).aspx>