$ENV{Name} = Value;If you really wanted to you could call the Win32API SetEnvironmentVariableA but there would be no advantage in doing so (and a lot of pain).

Note that Environment variables names are not case sensitive on Windows, but on UNIX/Linux they are. Changing an environment variable will not alter the setting in the registry (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment and HKEY_CURRENT_USER\Environment) and will only affect child processes of the current Perl program. This is the same effect as SetEnvironmentVariableA.