Subject: grep -vf <(<nothing>) filters all rows
From: Paul Eggert <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Date: Thu, 2 Jan 2020 01:04:21 -0800
List-Id: <debbugs-submit.debbugs.gnu.org>

> I have to pre-check for an empty set before passing it to grep:
> ...
> Workaround:

You're right that the empty pattern matches every line, since every line has an
empty string in it somewhere. This is considered to be a feature of grep, not a
bug. As you have a workaround I'm closing the bug report.