I just test for version strings. e.g. BASH_VERSION. It isn't ideal or robust but gets the job done depending on your requirements. There is no generally great solution.
There are scripts that make better guesses but there aren't any that are meant for use in a library or that do fine-grained feature detection. Something like that is on my todo list for some day. https://www.mirbsd.org/cvs.cgi/contrib/code/Snippets/getshver?rev=HEAD http://www.in-ulm.de/~mascheck/various/whatshell/whatshell.sh.html http://stchaz.free.fr/which_interpreter -- Dan Douglas
