bug#8231: Bug in the linux command: tail

[Roger N. Clark]

Eric Blake wrote:
> On 03/11/2011 10:03 AM, Roger N. Clark wrote:
>
> > Tail with a line count option with multiple files fails.
> >
> > For example:
> >
> > tail -3 foo.txt
> > f
> > d
> > s
> >
> > works, but
> >
> > tail -3 foo.txt  csh.cshrc
> > tail: option used in invalid context -- 3
>
>
> Thanks for the report.  At first, I was about to claim that this is not
> a bug in GNU coreutils, but a difference in levels of POSIX compliance.
>
> But digging further shows this in the NEWS file:  Back in coreutils 5.90:
>
> ** Bring back support for `head -NUM', `tail -NUM', etc. even when
>   conforming to POSIX 1003.1-2001.  The following changes apply only
>   when conforming to POSIX 1003.1-2001; there is no effect when
>   conforming to older POSIX versions.
>     tail -[NUM][bcl][f] [FILE]
>
> Basically, POSIX 2001 and newer does _not_ require -3 to be parsed as a
> valid option (rather, the POSIX spelling is -n -3), so GNU coreutils is
> supporting -3 as an extension.
>
> Then I looked at the actual POSIX 2008 wording:
> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/tail.html
>
>     tail [-f] [-c number|-n number] [file]
>
> That is, POSIX states that it is only portable to supply at most one
> filename, so the fact that GNU tail can support multiple files is
> already an extension, whether or not you also mix in the GNU extension
> of supporting -3 as an option.
>
> You can work around it by using: 'tail -n -3 file1 file2'
>
>
> > This works on HP-UX.
>
>
> Since we're already dealing with two GNU extensions, I don't see why we
> can't be nice and make the shorter syntax work the way HP-UX is doing
> things.  Patches welcome!

Eric,

Thank you for the quick reply.  I'm fine with needing to say -n -3.
Perhaps the man page needs to be clearer, so should be changed from the current:

       -n, --lines=N
              output the last N lines, instead of the last 10

to something like:

       -n N, --lines=N
              output the last N lines, instead of the last 10

A test showed no difference between -n -3 and -n 3.

Thanks!
Roger