Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!munnari.oz.au!metro!news
From: jimr@metro (Jim Richardson)
Newsgroups: comp.sys.apollo
Subject: Re: problems piping into 'tail'
Summary: May be an interaction between tail and DM, dependent on number of lines
Message-ID: <1990Aug1.022258.7408@metro.ucc.su.OZ.AU>
Date: 1 Aug 90 02:22:58 GMT
References: <2011@ns-mx.uiowa.edu>
Sender: jimr@maths.su.oz.au (Jim Richardson)
Organization: Dept of Pure Mathematics, University of Sydney
Lines: 38

In article <2011@ns-mx.uiowa.edu>, jlhaferman@l_cae07.icaen.uiowa.edu (Jeffrey
Lawrence Haferman) writes:
> 
> SR 10.2, /bin/csh is my shell, I can't get
> 
>    history | tail -15
> 
> to work.  'history' works fine, tail <filename> works
> fine, I can't get the pipe to work.  Ideas?
> 
> (I don't get an error back, just seems to wait a little
>  while, and then I get a prompt back.)

I haven't observed this problem with history: perhaps it depends on how
many lines the history contains.  However, I have similar problems with
commands like

	tail -300 syslogd.log

where syslogd.log is a logfile for syslogd, and therefore constantly open for
write, if it's important (that's why tail is needed instead of cv).

If I ask tail for only say 250 lines, all is well.  But over about 300, the
command sometimes just sits there until interrupted, and sometimes as Jeffrey
reports it pauses then comes back to the prompt with no output.

There seems to be some bad interaction between tail and the DM going on here.
If after the tail command has failed, you push and pop the pad in which it
was executed, you sometimes see very odd changes: some of the lines that tail
should have produced appear and/or disappear.  In fact, the pad seems to be
in a very unstable and inconsistent state.

Redirection of output via e.g. "tail -300 syslogd.log" > /tmp/slog succeeds
correctly.  Is that also true for Jeffrey's history example?
--
Jim Richardson
Department of Pure Mathematics, University of Sydney, NSW 2006, Australia
Internet: jimr@maths.su.oz.au  ACSNET: jimr@maths.su.oz  FAX: +61 2 692 4534