Gentoo ebuilds are parsed as bash, so no, there is no practical difference in this case. It's possible some external tool tried to implement its own parser for ebuilds, and did an incomplete job, but I am not aware of any tools which could not handle this.
its ebuild is EAPI="8" but said some error msg
i just don't understand
currently this thing is part of php use flag 'cdb' , i mean no other stuff requires this pkg
but just its error msg i can't understand
hackers - make sth real
academics - read sth said to be real
emerge --pretend --verbose dev-db/cdb seems fine here. You have been here long enough that I should not need to remind you of good troubleshooting practice, but I will: if you have a problem, post the output that shows the problem. I cannot explain to you an error message that I cannot see.