Re: Suggestion: Keep headings when sorted

[Assaf Gordon]

Hello,

On 2020-01-21 2:14 a.m., Mattias Johansson wrote:
> I often find that I want to keep one or a few lines untouched by sort, and end 
> up using something like this:
>
> $ awk 'NR == 1; NR > 1 { print $0 | "sort" }'
>
> It would be handy if sort had an option for 'number of heading lines' or 
> similar!
>
> I imagine something like this:
>
> $ sort -H  # keeps first line in place while sorting the rest

Adding "skip-header" support to GNU sort has been requested and
discussed several times in the past (including by me, seven years
ago...).

The decision was that such functionality can be easily achieved
using existing tools.

For some more details and past discussions, please see:
https://www.gnu.org/software/coreutils/rejected_requests.html#sort
https://lists.gnu.org/archive/html/coreutils/2013-01/msg00027.html
https://lists.gnu.org/archive/html/coreutils/2014-11/msg00022.html
https://lists.gnu.org/archive/html/coreutils/2015-10/msg00102.html

---

The simplest method is:

    $ ANY-PROGRAM | ( sed -u 1q ; sort )

This is slightly simpler and shorter than the above "awk" method.
It requires GNU sed for the "-u/--unbuffered" option.


The above sed+sort invocation can be made into a shell function:

      sorth() { sed -u 1q ; sort "$@"; }

And then use "sorth" instead of "sort"
(nothing the main difference is that "sort" can take input files on the
command line, while "sorth" must take the input from STDIN).

---

Change "1q" to "3q" or other values to keep more than one line of
headers at the top of the input.

The above shell function can be improved into:

   sorth() { num=$1 ; shift ; sed -u ${num}q ; sort "$@"; }

To accept the number of header lines as a (required) first parameter,
e.g. the following will keep the first the values intact and randomize 
the remaining 7:

   seq 10 | sorth 3 -R

---

If all else fails, and such a sort-header program is still needed,
I can offer my own attempt at such a perl-wrapper script,
which I wrote before knowing about the "sed/sort" method:
 https://github.com/agordon/bin_scripts/blob/master/scripts/sort-header.pl

Hope this helps,
regards,
  Assaf