String variables containing information that an operating system uses to control services and applications. The PATH and TEMP variables used in the autoexec.bat file in MS-DOS were early examples of environment variables. Microsoft Windows NT and Windows 2000 offer a more extensive selection.
For example, environment variables for Windows NT include the following:
Graphic E-4. Environment variables of Windows NT.
You can view and specify environment variables in Windows NT and Windows 2000 by using the System utility in Control Panel. Environment variables may be used in logon scripts by enclosing them within percent symbols; for example, %USERNAME% contains the currently logged on user name.
The System utility in Control Panel shows only a portion of the system environment variables defined on a system running Windows NT or Windows 2000.