bug#17022: Dosen't work properly option -u of uniq

[Pádraig Brady]

On 03/17/2014 05:06 AM, Александр Ботов wrote:
> Good day!
> 
> I've tried to use option -uD to discard the first repeated line as it written 
> in info, but it discards the last one.
> 
> In the info said that for this purpose I should use option -u not by itself, 
> but doesn't said what dose it mean. Could you said (and may be add to the 
> man/info) how to use option -u to discard _the first_ repeated line, please?
> 
> I use Scientific Linux SL release 5.4 (Boron), Linux version 
> 2.6.18-92.1.10.el5.mk8 (gcc version 4.1.2 20070626 (Red Hat 4.1.2-14)), uniq 
> (GNU coreutils) vesion 5.97.
> 
> Best regards, Alexander.

So the description in question is:

`-u'
`--unique'
     Discard the first repeated line.  When used by itself, this option
     causes `uniq' to print unique lines, and nothing else.

Showing all combinations of options with the particular
one in question at the end shows that we always discard
later lines in a group.

$ cat in

$ for o in '' '-d' '-D' '-u' '-ud' '-dD' '-uD'; do echo "$=== $o ===="; 
src/uniq $o -f1 in; done
1 a
2 a
3 a
1 b
2 b
1 c
$===  ====
1 a
1 b
1 c
$=== -d ====
1 a
1 b
$=== -D ====
1 a
2 a
3 a
1 b
2 b
$=== -u ====
1 c
$=== -ud ====
$=== -dD ====
1 a
2 a
3 a
1 b
2 b
$=== -uD ====
1 a
2 a
1 b


Now discarding a single item from a repeated group is unusual,
whether one is discarding the first or the last.
We should at least clarify the documentation, but please
consider adjusting the sort(1) to select between these.
I.E. for the above example: sort -r in -k2,2

thanks,
Pádraig.