Thank you both for the suggestion on what to do to with -I (as it happens, the NetBSD shell will exit if it gets 50 EOF's with no command between (I'm not certain, and haven't tested it, but I suspect empty lines and lines containing only comments might not count as commands, but something as simple as : would).
That wasn't something I knew before, and it isn't documented, but it is what the code does... But dealing with -I wasn't really the question, I'd appreciate opinions on handling -n though (not so much in interactive shells, David Holland's suggestion seems fine for that, and entirely reasonable) - but for non-interactive shells (scripts that set -n in weird places, rather than ones invoked as "sh -n script" which are easy to deal with.) kre
