Weird behaviour (possibly bug) of sort

[Kilian Hekhuis]

Dear coreutils maintainers,

I have found very weird behaviour in GNU sort on Linux (coreutils 7.4),
and I'm wondering if it's me doing something wrong, or whether there's a
bug in there.

I have this input file:
20       6      1234XX
12       10     1234XX
14       13     1234AA


I would like to sort on the third column first, then on the second column,
but numerical, not ASCII. I figured this should do it:

sort -k3,3 -k2,2n inp.txt

However, the result comes out wrong:

14       13     1234AA
12       10     1234XX
20       6      1234XX


Although the third column is sorted the way I want, the second isn't: 6
should come before 10. So I tried something slightly different:

sort -n -k3,3f -k2,2 inp.txt

But no such luck: though the 'f' triggers ASCII sorting, it also somehow
prevents the second -k receiving the global -n. Then I tried to switch the
columns in the input file:

20       1234XX      6
12       1234XX      10
14       1234AA      13

And what do you know? Both "-k2,2 -k3,3n" and "-n -k2,2f -k3,3" produce
the right, expected output:

14       1234AA      13
20       1234XX      6
12       1234XX      10

I'm a bit lost here, as this is behaviour that is certainly not
documented, and I would think this is a bug.

Best regards,


Kilian Hekhuis