Why does bash behave differently, when it is called as sh?

Question

I have an ubuntu machine with default shell set to bash and both ways to the binary in $PATH:

$ which bash
/bin/bash
$ which sh
/bin/sh
$ ll /bin/sh
lrwxrwxr         


        

Answer 1

When bash is invoked as sh, it (mostly) restricts itself to features found in the POSIX standard. Process substitution is not one of those features, hence the error.