bug#27368: Minor concern: Confusing tail warning

[Charlie Hagedorn]

Hi!

Thank you for maintaining such useful and reliable tools.

Today I came across an unexpected warning in tail. The warning is intended
to handle this case:

[:~]$ tail -f
tail: warning: following standard input indefinitely is ineffective

which is both important and fun.

Today, however, I was surprised to see it appear in this context:

[:~]$ tail -f < /dev/ttyUSB0  > data.dat
tail: warning: following standard input indefinitely is ineffective

The warning was confusing and perhaps inappropriate, as this call actually
*does* something, and is very effective at doing what I want; streaming the
port's output into data.dat.

(Importantly, for reasons I don't yet understand, tail -f /dev/ttyUSB0 >
data.dat does not reliably tail the port; it redirects only one line of
output instead of a continuous stream).

System is Debian Jessie -- coreutils v8.23-4.

Thanks!

Charlie