How can I test for POSIX compliance for shell scripts?

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http://unix.stackexchange.com – Probably the main thing that this website has taught me so far is the importance of writing portable shell scripts. Considering that POSIX is the closest thing to a common standard between all unices, I'm interested in knowing if there's a shell that supports it exclusively. While most modern shells provide support for POSIX (and will run POSIX compliant scripts without any problem), they don't do a good job at pointing out non compliant features. Is there any shell that implements POSIX and POSIX only, in such a way that it'd throw an error for any non compliant feature? EDIT I want to cl (HowTos)