GNU bug report logs - #9370
"tail -f -1" should work

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Eli the Beareded <gnu-bugs <at> panix.com>
To: bug-coreutils <at> gnu.org
Subject: "tail -f -1" should work
Date: Thu, 25 Aug 2011 02:15:39 -0400 (EDT)

$ tail --version
tail (GNU coreutils) 8.5
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Paul Rubin, David MacKenzie, Ian Lance Taylor,
and Jim Meyering.
$
$ tail -f -1 some.log
tail: option used in invalid context -- 1
$

On any other system I have used the -NUM option can be used with
the -f option to specify how many lines of the file as-is to print
before starting to follow it for updates.

With this version of tail, it always prints ten lines and then
starts the follow.

Elijah

Message #8 received at 9370 <at> debbugs.gnu.org (full text, mbox):

From: "Voelker, Bernhard" <bernhard.voelker <at> siemens-enterprise.com>
To: Eli the Beareded <gnu-bugs <at> panix.com>, "9370 <at> debbugs.gnu.org"
	<9370 <at> debbugs.gnu.org>
Subject: RE: bug#9370: "tail -f -1" should work
Date: Thu, 25 Aug 2011 16:21:03 +0200

Eli the Beareded wrote:
> $ tail -f -1 some.log
> tail: option used in invalid context -- 1
> $

I think you wanted this:
$ tail -f -n1 some.log

The syntax is explained quite nice in recent versions:

    -n, --lines=K            output the last K lines, instead of the last 10;
                             or use -n +K to output lines starting with the Kth
  ...
  If the first character of K (the number of bytes or lines) is a `+',
  print beginning with the Kth item from the start of each file, otherwise,
  print the last K items in the file.  K may have a multiplier suffix: ...

Have fun,
Berny

Message #11 received at 9370 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eli the Beareded <gnu-bugs <at> panix.com>
Cc: 9370 <at> debbugs.gnu.org
Subject: Re: bug#9370: "tail -f -1" should work
Date: Thu, 25 Aug 2011 11:48:45 -0700

On 08/24/11 23:15, Eli the Beareded wrote:
> On any other system I have used the -NUM option can be used with
> the -f option to specify how many lines of the file as-is to print
> before starting to follow it for updates.

The interaction between -NUM and other options is so complicated
and unportable (different editions of the POSIX standards
disagree!) that GNU 'tail' is fairly conservative about where it
allows -NUM.  It might be nice to add support for your particular usage,
if someone wants to write the code, but it'll require some care to make
sure it doesn't run afoul of existing usage or standard in some other way.

In the meantime I suggest using "tail -f -n NUM", as that's standard
and portable these days.

Message #14 received at 9370 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Eli the Beareded <gnu-bugs <at> panix.com>, 9370 <at> debbugs.gnu.org
Subject: Re: bug#9370: "tail -f -1" should work
Date: Tue, 13 Sep 2011 14:18:03 +0200

tags 9370 notabug wishlist
thanks

Paul Eggert wrote:
> On 08/24/11 23:15, Eli the Beareded wrote:
>> On any other system I have used the -NUM option can be used with
>> the -f option to specify how many lines of the file as-is to print
>> before starting to follow it for updates.
>
> The interaction between -NUM and other options is so complicated
> and unportable (different editions of the POSIX standards
> disagree!) that GNU 'tail' is fairly conservative about where it
> allows -NUM.  It might be nice to add support for your particular usage,
> if someone wants to write the code, but it'll require some care to make
> sure it doesn't run afoul of existing usage or standard in some other way.
>
> In the meantime I suggest using "tail -f -n NUM", as that's standard
> and portable these days.

I've marked this as a wishlist item.

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