On Tue, Jul 01, 2025 at 02:28:48PM -0500, Eric Blake wrote: > On Fri, Jun 27, 2025 at 08:51:10AM -0700, Jim Meyering wrote: > > > > > > > > [1] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/tail.html > > > > > > tail -r comes from the BSDs. > > > Also the BSDs don't have tac(1) which overlaps in functionality quite a > > > bit. > > > I'm a bit surprised -r was added by POSIX, but fair enough. > > > > "Surprised" is putting it lightly. I am disappointed and am tempted to > > push back and to delay encumbering GNU tail with -r. > > That is an option no GNU system needs, since they've all had tac since > > before 1992-era textutils. > > > > I've Cc'd Eric Blake, in case someone wants to propose adding tac to > > POSIX in spite of the fact that the BSDs still lack it. > > I'll bring up this topic at the next Austin Group meeting. > > At any rate, it looks like tail -r was added due to this bug report in > 2014 (sadly, it is no longer an option to ask Jorg Schilling why he > wanted it standardized) > https://www.austingroupbugs.net/view.php?id=877 > > But I did ask at the time (with no answer) why we went with 'tail -r' > instead of 'tac'.
Correction - my comment asking why we didn't go with tac was dated 2014-10-23 at 22:44, https://www.austingroupbugs.net/view.php?id=877#c2428 but the wording to move forward with 'tail -r' was amended in place, so even though the proposed wording was in place before my question at 2014-10-23 15:18, it was later amended on 2014-10-30 to add the Rationale on why 'tail -r' provides a potential algorithmic improvement over 'tac | head -n' when it comes to amount of memory consumed. https://www.austingroupbugs.net/view.php?id=877#c2425 -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org
