Major Section: HISTORY
Examples: :ubt :max ; undo back through the most recent command ; (which just means undo the most recent command) :ubt :x ; same as :ubt :max :u ; same as :ubt :max with no questions asked :ubt fn ; undo back through the introduction of fn ; (including all the other events in fn's block) :ubt 5 ; undo back through the fifth command executed :ubt (:max -4) ; undo back through the most recent five commands :ubt (:x -4) ; undo back through the most recent five commandsSee command-descriptor.
Ubt takes one argument, a command descriptor, and undoes the
:x) through the one described.
Pbt will print the commands that
Oops will undo the undo. See oops.
Ubt can cause errors or queries. To avoid these, see ubt!.
It is important to remember that a command may create several
events. That is, the command that introduces
fn1 may also introduce
fn2. Undoing the command that created either of these will undo
them both. The events created by a command constitute the command's
``block'' and we can only undo entire blocks. Use
pcb to print the
command block of a command if you wish to see what will be lost by
undoing the command.
Ubt will not undo into ``prehistory''.
:Ubt 1 will undo all of your
:ubt -5 will cause an error, warning you that
cannot undo system initialization.