Pipeline question (echo hello | echo $(cat))

[Matthew Flaschen <matthew.flaschen@xxxxxxxxxx>]

I have a question about command lines like:

echo hello | echo $(cat)

Both bash and dash give:

hello

but zsh executes it in the other order, so errors:

cat: -: Input/output error

This occurs even when zsh is run as sh.

Can anyone shed some light on this?  Is either behavior specified by POSIX?

Matt Flaschen