Sort using keys

iggi · 11-06-2007, 09:22 AM

Hello,

I've read about 'sort' and am unable to figure out the difference between eg.

"sort -t: -k 2,3" and "sort -t: -k 2"

say <file> contains:

Code:

[root@localhost ~]# cat file
x:1:1:operator:/root:/sbin/nologin
x:1:1:oink:/bin:/sbin/nologin

sort -t: -k 2,3 gives

Code:

x:1:1:oink:/bin:/sbin/nologin
x:1:1:operator:/root:/sbin/nologin

and

sort -t: -k 2

does the same job. I would expect "-k 2,3" NOT to look at the following characters but it still does (oink is put before operator). I read -k 2 processes from field 2 till the end so that result is as expected.

Any idea?

thanks, Dirk

Tinkster · 11-06-2007, 11:18 AM

-k 2,3 will ONLY sort by 2 and 3
-k 2 will sort by everything from the 2nd field onward

If you want to sort by just the 2nd field it's
-k 2,2

The whole line is a "bonus", I guess, because there's
no sort-order defined past your description.

Cheers,
Tink

iggi · 11-07-2007, 01:12 AM

Quote:

Originally Posted by Tinkster

-k 2,3 will ONLY sort by 2 and 3
-k 2 will sort by everything from the 2nd field onward

If you want to sort by just the 2nd field it's
-k 2,2

The whole line is a "bonus", I guess, because there's
no sort-order defined past your description.

Cheers,
Tink

Thanks. Although it's not really an issue I'm trying to understand the difference between "-k x" , "-k x,x" and "-k x,y".

From what I see there's no difference at all and suprisingly it doesn't seem usefull (except eg. "-k x -k y" when column x and y aren't adjacent)

Code:

[root@localhost ~]# cat file
vb test cfg
vb test abc
ab cd   ef
zz zzz zz
vb test bdd
kk zzz zz
[root@localhost ~]# sort -k 1 file
ab cd   ef
kk zzz zz
vb test abc
vb test bdd
vb test cfg
zz zzz zz
[root@localhost ~]# sort -k 1,1 file
ab cd   ef
kk zzz zz
vb test abc
vb test bdd
vb test cfg
zz zzz zz
[root@localhost ~]# sort -k 2 file
ab cd   ef
vb test abc
vb test bdd
vb test cfg
kk zzz zz
zz zzz zz
[root@localhost ~]# sort -k 2,2 file
ab cd   ef
vb test abc
vb test bdd
vb test cfg
kk zzz zz
zz zzz zz

It's all the same and even for "-k 2,2" the previous columns get sorted (for same values of key 2). Even "-k 2,3" produces the same output.

Dirk

iggi · 11-07-2007, 01:18 AM

I guess the only reason would be when appending options like 'g' or 'n' to specify the type of sorting. Then you could say eg. column 2 and 3 contain numbers but the rest is just text:

-k 2,3n

Tinkster · 11-07-2007, 01:31 AM

Those are fair enough comments. But just go the other way around;
what behaviour would you expect for the other cases? There's no
real way (or need) to "unsort" things if there's no second condition
that is indeed of a different type (or direction) or in non-adjacent
columns ... of course you can also go like

sort -k3,3g -k1,2r -k4

and the likes, which should be bear quite different results.

Cheers,
Tink