SET

Displays, sets, or removes cmd.exe environment variables.
 
SET [variable=[string]]
 
  variable  Specifies the environment-variable name.
  string    Specifies a series of characters to assign to the variable.
 
Type SET without parameters to display the current environment variables.
 
SET command invoked with just a variable name, no equal sign or value
will display the value of all variables whose prefix matches the name
given to the SET command.  For example:
 
    SET P
 
would display all variables that begin with the letter 'P'
 
SET command will set the ERRORLEVEL to 1 if the variable name is not
found in the current environment.
 
SET command will allow an equal sign (=) in the value of an environment
variable in any position other than the first character.