Re: Sort with header/skip-lines support

[Pádraig Brady]

On 01/10/2013 09:57 PM, Assaf Gordon wrote:
> Hello,
>
> I'd like to re-visit an old issue: adding header-line/skip-lines support to 
> 'sort'.
>
> It has been discussed few times in the past, but IMHO the suggested workarounds 
> fall short:
> 1. Sometimes using 'bash' specific constructs [1]
> 2. No error checking (e.g. running head/tail/sed without checking for errors)
> 3. Using multiple input files is convoluted.
> 4. Suggestions work for regular files, but not for pipes [2].
>
> The attached draft patch is based on Jim Hester's patch [3], rebased to the 
> latest sort, with some fixes and tests.
> It seems to work fine, except one glaring omission: it only works when output 
> is STDOUT because creating the output file is a brute-force ugly hack.
>
> The syntax is
>    sort --skip-lines=N [other options]

That's a bit ambiguous and might suggest that the header line
was not output after the sort? Maybe keep consistent with
`join` and `numfmt` and use --header.

> The two tests are:
>    make check TESTS=tests/misc/sort-skip-lines SUBDIRS=.
>    make check TESTS=tests/misc/sort-skip-lines-bigfiles SUBDIRS=. 
> RUN_EXPENSIVE_TESTS=yes
>
> If this is something you are willing to consider, I'm happy to hear comments 
> and suggestions and improve it.
>
> Alternatively, perhaps this is a good candidate for a "contrib" script, but I'm 
> not sure how do go about developing a shell script that is posix compliant, has robust 
> error checking, and still be a full 'drop-in' replacement for sort (many options 
> combinations).
>
> Thanks,
>   -gordon
>
> [1] - bash work-around: 
> http://lists.gnu.org/archive/html/coreutils/2010-11/msg00084.html
> [2] - no pipe support: 
> http://lists.gnu.org/archive/html/bug-coreutils/2007-07/msg00215.html

Note the pipe issue might be handled with `stdbuf -i0 head ...`
but head doesn't use stdio so that won't work.
But recent sed can be used for this like: `seq -u 1q`
http://git.sv.gnu.org/gitweb/?p=sed.git;a=commit;h=737ca5e
Note that commit is 4 years old, but only recently released sed 4.2.2 contains 
it.

> [3] - Jim's patch: 
> http://lists.gnu.org/archive/html/coreutils/2010-11/msg00091.html

Thanks for collating the previous threads on this subject.

I'm on the fence on how warranted this is TBH.
We'd need stronger arguments for it I think.

thanks,
Pádraig.