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

[Cedric Blancher]

On 24/05/2009, Roland Mainz <roland.mainz at nrubsig.org> wrote:
>
>  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 --

I agree that this is a bug in SunOS5 tail. OSX, AIX and FreeBSD tail
+4r return identical output as tail +4 reversed.

As a historical note, AIX uses the same OSF derived sources as SunOS5
but IBM fixed this bug in 5L years ago.
-- 
Cedric Blancher <cedric.blancher at googlemail.com>
Institute Pasteur