Usage: SET [-][<variable name> [<value>]]
  Sets a specified variable to a given value.  If SET is used
  with no parameters, all variables and their current settings
  are listed.  If SET is used with a variable name and no value,
  that variables current setting is listed.  If a - preceeds
  a variable whose value is a string of text, it sets that
  variable to nothing.

See also:
  HELP SET ? for a list of all variables