I know this is a silly question, but i don't know the answer and i
figure that people here will....

I can do:

tail -f messages | grep -v assist

But why doesn't this work:

tail -f messages | grep -v assist | grep -v cron

And so on with a few more greps as wanted?

I can't work it out, maybe my brain ain't working properly......

Cheers
Ade

when grep writes to a tty, it does line buffering.  when it writes to
a pipe, it does block buffering (4 KiB?).  if you install GNU grep,
you can override this behaviour with --line-buffered

--
Kjetil T.

Pasil

In what way does that not work?

Since the output of the first grep is not to a terminal, it will be
buffered.  The second grep won't see anything until there is enough
in the buffer (maybe something like 1K or so of output).  The effect
is that there may be long periods with no output from the final
stage, followed by a whole bunch of lines.

That just increases the number of buffering layers.

It will be more responsive to use

        tail -f messages | egrep -v 'assist|cron'

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (SunOS)

iD8DBQFALkCevmGe70vHPUMRAhL2AKCIVZVgXFltJxYAyaw3gCUI0bsHDACgsDr+
zeiqEv9xi+31T9RF0MHn18Q=
=kGKK
-----END PGP SIGNATURE-----

Thanks Neil et all, I hadn't put that together at all.

Ade