Usage: @ <expression>
  The @ command evaluates the given expression in "variable
  expression" mode.  This is the same mode used inside IF ()
  and WHILE ().  Normally it is used for variable assignment
  as it provides a nicer syntax than ASSIGN does in some
  contexts.  These are the same thing:

	@ foo = [bar]
	assign foo bar

  as are these:

	@ foo = C
	assign foo $C