SET

Displays, sets, or removes MS-DOS environment variables.

Note: MS-DOS environment variables: PROMPT and PATH 
commands use environment variables to save their information. 
Also, you can use environment variables to exchange information 
between your programs, especially batch programs.

In batch programs, environment variables can be expressed in 
this format: %env% . Then, to express a "%" mark, you should use 
this format: %% .

For more information, please refer to MS-DOS Help or Windows NT 
command line command help.