I will guess that your use of cat without a line end leaves ESS waiting for a prompt.
cat("b", "\n") would be the way to avoid that. The way to unfreeze ESS (and emacs more generally) is Ctrl-g Please put followup ESS questions on the ESS list ess-h...@stat.math.ethz.ch Rich [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.