From owner-freebsd-questions@freebsd.org  Wed Sep 27 22:20:19 2017
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Date: Wed, 27 Sep 2017 15:20:17 -0700
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To: freebsd-questions@freebsd.org
Subject: Re: Possible bug in tail(1)
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I agree with Matthias that the issue arises when 'tail -r' is reading
from a pipe.

I looked at the GitHub mirror and downloaded a few src tarballs around
recent commits to tail.

Building tail from:

https://github.com/freebsd/freebsd/tree/97a2ca501c7e9f07a80339a88fbb5a46977ae428

does not manifest the bug.

However, tail built from:

https://github.com/freebsd/freebsd/tree/2fef72832029bcc228a527dd9c423ba34a7490e9

does.  IANAE, but it appears the bug may have crept in during:

https://reviews.freebsd.org/D9067


HTH,

Jim