How to implement 'set -o pipefail' in a POSIX way - almost done, expert help needed

Question

I have to implement the BASH set -o pipefail option in a POSIX way so that it works on various LINUX/UNIX flavors. To explain a bit, this option enables the user to

Answer 1

Am I missing something?

my-script.sh

#!/bin/sh

set -e

cat app.log | grep 'ERROR' 

printf 'It will never print this.\n'

$ ./my-script.sh
cat: app.log: No such file or directory