$? and $! equivalents

This is probably going to be a forehead-slapper, but I can't find a
reference in either perlintro.com or http://docs.perl6.org/
(5to6-perlfunc or top-down)  for the equivalents of $? and $! in
P6.What are they?

I want to be able to "run" or "shell" programs, then examine return
codes and errors. (The immediate case is to see if a program name is
already in use by running  "which $progname". )