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.
> 
> 
> 

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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)
Windows Installer does support environment variables through [Environment](http://msdn.microsoft.com/en-us/library/windows/desktop/aa368369%28v=vs.85%29.aspx) table, but Visual Studio setup projects do not allow you to use it.

A solution is to use a different setup authoring tool which supports environment variables: <http://en.wikipedia.org/wiki/List_of_installation_software>

Another solution is to manually add it in Environment table by editing the MSI with [Orca](http://msdn.microsoft.com/en-us/library/windows/desktop/aa370557%28v=vs.85%29.aspx).

There's also the custom action approach you mentioned.