Re: tail +n does not work under Linux?

[Christophe LYON]

On 07.05.2009 19:49, Matthew Woehlke wrote:
> Christophe LYON wrote:
> > > > I am using coreutils-7.2, and I have just reproduced the issue with 
> > > > 7.3, under Linux RHEL 3 and 4.
> > >
> > > Also with Fedora 10's 6.12 package. The behavior change I think may 
> > > have been in 6.0 (it is probably in the changelog).
> >
> > I do remember that change, but I also thought that it had been 
> > reverted a few releases later.
>
> -<number> seems to work presently, +<number> doesn't.

This seems inconsistent to me. Am I the only one? :-)

> > > > Curiously, it works OK under Solaris 8.
> > > Are you talking about GNU coreutils here, or the Solaris tail? If the 
> > > behavior is different for GNU coreutils, that is probably a bug.
> >
> > Yes, GNU coreutils built under Solaris.
>
> Hmm. That sounds suspiciously like a bug, then. I don't think the 
> behavior should be different across platforms. (Time for one of the 
> maintainers to chime in...)
Well, I have re-read and tried doc kindly carbon-copied by A.Szmidt, and 
it seems that under Solaris coreutils default to an older POSIX version 
than under Linux.

But I still don't know how to know that at runtime. For instance 'tail 
--version' does not mention anything about that. It's probably not the 
right place to report, but I think there should be a most obvious way 
for the end-user to realize this issue.

> > But 'man tail' says:
> >        -n, --lines=N
> >               output the last N lines, instead of the last 10; or use 
> >               +N  to output lines starting with the Nth
> >
> > does it mean that '-n' is mandatory before a number? I interpreted it 
> > as  '-number'.
>
> I read it as, yes, -n is still required (but agree it isn't as clear as 
> it might be), especially given the blurb in the info doc. IOW I read 
> '+N' as replacing 'N', not as replacing '-n N' or '--lines=N'.

My understanding of this man fragment is that:
'-n 3' is equivalent to '--lines=3', and one can replace '3' by '+3'.

But I still don't see where '-3' is documented?


As mentioned earlier, at release 6.0 (approx), using '-3' stopped 
working. I remember I read the coretuils standard conformance doc at 
that time to understand the issue, and started modifying my scripts to 
use '-n 3' instead. Any a few coreutils releases later, I noticed '-3' 
worked again, but I guess I never understood why. So, I still don't :-)


Christophe.