Re: Sort with header/skip-lines support (original) (raw)

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From: Assaf Gordon
Subject: Re: Sort with header/skip-lines support
Date: Fri, 11 Jan 2013 11:10:29 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.4) Gecko/20120510 Icedove/10.0.4

Pádraig Brady wrote, On 01/10/2013 07:11 PM:

On 01/10/2013 09:57 PM, Assaf Gordon wrote: > > I'd like to re-visit an old issue: adding header-line/skip-lines support to > 'sort'. > > [...] > > [2] - no pipe support: > http://lists.gnu.org/archive/html/bug-coreutils/2007-07/msg00215.html

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.

Thanks for the tip.

The following indeed works with sed 4.2.2 ( on linux 3.2 ): $ ( echo 99 ; seq 10 ) | ( sed -u 1q ; sort -n )

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?).

> [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.

I'll collate the arguments as well :)

If the "sed" method works reliably, it leaves error checking: how to reliably check for error in such a pipe (inside a posix shell script)? The closest code I found is this: https://github.com/cheusov/pipestatus which seems very long.

So additional arguments are:

  1. robust error checking
  2. simplicity of use: if 'sort' had this option built-in, the following use cases would "just work". with sed+sort, it will require different invocations (and probably different pitfalls): a. one input file b. one input pipe c. multiple input files (without resorting to pipe, as this will cause 'sort' to use different amount of memory) d. specifying output file (with "-o")

Thanks, -gordon

As a side note, I have a hackish Perl script that wraps sort and consumes the first line, and it's basically works-for-me kind of script - but I just wish it wasn't necessary: https://github.com/agordon/bin_scripts/blob/master/scripts/sort-header.in