Re: Sort with header/skip-lines support

[Pádraig Brady]

On 01/11/2013 07:19 PM, Assaf Gordon wrote:
> Hello Pádraig,
>
> Your suggestions work for all the cases I needed, so essentially there's 
> already a way to do sort+header - much appreciated!
>
> Pádraig Brady wrote, On 01/11/2013 01:13 PM:
> > On 01/11/2013 04:10 PM, Assaf Gordon wrote:
> > > Pádraig Brady wrote, On 01/10/2013 07:11 PM:
> > >
> > > The following indeed works with sed 4.2.2 ( on linux 3.2 ):
> > >      $ ( echo 99 ; seq 10 ) | ( sed -u 1q ; sort -n )
> > >
> > > [2] - no pipe support: 
> > > http://lists.gnu.org/archive/html/bug-coreutils/2007-07/msg00215.html
> > > But I'm wondering (as per the link above [2]) if this is posix compliant and 
> > > stable (i.e. can this be trusted to work everytime, even on non-linux 
> > > machines?).
> >
> > No `sed -u` with this functionality is not portable.
> > Though it's more portable than `sort --header`
> > given that it already exists :)
>
> Sorry for nitpicking, but just to verify:
> "sed -u" is a GNU extension, hence not portable by definition.
> But what I meant to ask:
> If I install GNU sed + GNU sort on any machine (e.g. MAC OSX), would it work in 
> a reliable way?
> Eric Blake's email seemed to suggest this will never be guaranteed to work 
> (even if it works in practice) due to sharing pipes between processes.

Eric's point I think is that there is no guarantee
that processes will not read too much from the pipe.
But if you have GNU sed >= 4.2.2 in place then it
should work fine, as he alluded to in the sh exception.

thanks,
Pádraig.