echo first $$ >&2 | bash -c 'echo second $$' first 30551 second 28057
but eval 'echo first $$' >&2 | eval 'echo second $$' first 30551 second 30551
echo first $$ >&2 | bash -c 'echo second $$' first 30551 second 28057
but eval 'echo first $$' >&2 | eval 'echo second $$' first 30551 second 30551