"tail +r<number>" not equivalent to "tail +<number> | rev -l" ?

[Roland Mainz]

Hi!

----

[The following is either a PSARC or OS/Net gatekeeper question - I don't
know it exactly and therefore both end-up in the CC: field]
During PIT (=PreIntegration Testing) for ksh93-integration update2
(which includes an opensource replacement for /usr/bin/tail and
/usr/xpg4/bin/tail (note that both are built from the same source) - see
http://arc.opensolaris.org/caselog/PSARC/2009/249/20090420_roland.mainz.2)
we hit a bug with "tail -r/+r" and during fixing it we've hit the
following issue:

SXCE B110 tail(1) manual page defines "tail"'s "-r" option like this:
-- snip --
 -r     Reverse. Copies lines  from  the  specified  starting
        point in the file in reverse order. The default for r
        is to print the entire file in reverse order.
-- snip --

PSARC/2009/249 defines it the same way but with a shorter description:
-- snip --
  -r, --reverse   Output lines in reverse order.
-- snip --

Both AFAIK are thought that option "-r" works like "tail -<number> | rev
-l" ("rev -l" outputs the incoming lines in reverse order). The
/usr/bin/tail+/usr/xpg4/bin/tail commands in SXCE B110 does this
correctly when I use something like "-<number>r", for example:
-- snip --
$ print "1\n2\n3\n4\n5\n6" | /usr/xpg4/bin/tail
-4r                                                 
6
5
4
3
$ print "1\n2\n3\n4\n5\n6" | /usr/xpg4/bin/tail -4 | rev
-l                                         
6
5
4
3
-- snip --

All other combinations for "-<number>" are identical between "tail
-<number>r" and "tail -<number> | rev -l", too.


However this is _not_ true when I use "tail +<number>r" compared to
"tail +<number> | rev -l". In that case the output differs:
-- snip --
$ print "1\n2\n3\n4\n5\n6" | /usr/xpg4/bin/tail
+4r                                                 
6
5
4
3
2
$ print "1\n2\n3\n4\n5\n6" | /usr/xpg4/bin/tail +4 | rev
-l                                         
6
5
4
-- snip --

Both outputs differ and I belive this is simply a bug in the current
SXCE implementation.

Question to gatekeepers: How should I handle this issue ? Should we...
a) ... treat this as bug and fix it with the upcoming ksh93-integration
putback
  or
b) ... make the AST/ksh93 builtin behave _exactly_ as the current SXCE
implementation of /usr/bin/tail+/usr/xpg4/bin/tail and fix this bug with
a later putback
  or
c) ... declare that this is not a bug and keep the inconsistent
behaviour of "tail +<number>r" vs. "tail +<number> | rev -l".

AFAIK I would prefer [a] but I have a patch for [b], too. [c] is IMO not
really an option since makes option "r" behave in an inconsistent way.

----

Bye,
Roland

-- 
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