bug#22109: Sort gives incorrect order when changing delimiters

[Eric Blake]

tag 22109 notabug
thanks

On 12/07/2015 08:36 AM, Ed Brambley wrote:
> The following problem came to light following a StackOverflow question [1].
> The lexical ordering of sort appears to depend on the delimiter used, and I
> believe it shouldn't. As a minimal example:

Thanks for the report.  However, you have not found a bug in sort, only
in your misuse of the command line and in your incorrect assumptions.

Let's investigate further with the --debug option:

> 
> ### Correct ordering ###
> $ printf "1,a,1\n2,aa,2" | LC_ALL=C sort -k2 -t,
> 1,a,1
> 2,aa,2

$ printf '1,a,1\n2,aa,2' | LC_ALL=C sort -k2 -t, --debug
sort: using simple byte comparison
1,a,1
  ___
_____
2,aa,2
  ____
______

You are comparing the string "a,1" with "aa,2"; so the relative relation
between ',' and 'a' matters.

> 
> ### Incorrect ordering by replacing the "," delimiter by "~" ###
> $ printf "1~a~1\n2~aa~2" | LC_ALL=C sort -k2 -t~
> 2~aa~2
> 1~a~1

Same goes for here.

$ printf '1~a~1\n2~aa~2' | LC_ALL=C sort -k2 -t~ --debug
sort: using simple byte comparison
2~aa~2
  ____
______
1~a~1
  ___
_____

You compared the string "aa~2" with "a~1".


> 
> I think this is because, in ASCII, "," < "a" < "~".

Yes, so you saw exactly what you asked for.  But what you asked for
("sort starting from the second delimiter through to the end of the
line") is probably not what you wanted.  It sounds like you wanted "sort
on ONLY the second delimiter", which is spelled differently:

$ printf '1~a~1\n2~aa~2' | LC_ALL=C sort -k2,2 -t~ --debug
sort: using simple byte comparison
1~a~1
  _
_____
2~aa~2
  __
______


Note that there is a very distinct difference between '-k2' and '-k2,2';
only the latter one limits the sort to JUST the second key ("a" vs.
"aa", regardless of delimiter), while the former slurps in the rest of
the line such that the spelling of the delimiter affects the result.

I'm marking this as not a bug in the database, but feel free to add
further comments.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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