In Windows, the setx command allows storing environment variables in the Windows registry on a per-user or system basis. A problem arises when it is desired to remove such variables entirely. Setting a blank value does not work.

Example: assume one previously set the environment variable CC to the Intel C compiler like:

setx CC icx

Now the problem is, you’d like the system to fall back to using whatever default C compiler is on the Windows system. The existing variable is visible in PowerShell via:

Get-ChildItem Env:CC

But trying to remove the variable with PowerShell command

Remove-Item Env:FC

is only effective for this PowerShell session. The old value of CC comes back upon opening a new PowerShell.

To permanently remove the “setx” variable, we must remove it from where it’s stored in the Windows registry. For this example of wanting to delete enviornment variable CC, do from PowerShell:

reg delete "HKCU\Environment" /v CC

Optionally, confirm deletion with PowerShell:

Get-ChildItem Env:CC