test -nt and -ot ignore the subsecond part of file timestamps

[Sam Kendall]

Example on Linux (RHEL 8):

$ touch a; sleep 0.1; touch b
$ ls --full-time a b
-rw-r--r-- 1 kendall staff 0 2019-12-05 13:41:43.483652556 -0500 a
-rw-r--r-- 1 kendall staff 0 2019-12-05 13:41:43.585652744 -0500 b
$ if [ a -ot b ]; then print older; fi
$ if [[ a -ot b ]]; then print older; fi
$

The last two commands should have printed "older".

$ print $KSH_VERSION
@(#)MIRBSD KSH R56 2018/01/14
$ uname -sr
Linux 4.18.0-80.el8.x86_64

R49 on Cygwin and R46 on RHEL 7 have the same behavior.

[Sam Kendall (sckendall)]

-nt and -ot are Korn extensions, so there's no POSIX standard behavior to conform to.

On RHEL 7 and 8, ksh93 and bash do *not* have the bug. On my old-ish version of Cygwin, bash *does* have the bug.

[Thorsten Glaser (mirabilos)]

My first reaction was “yes, there are operating systems with sub-second timestamps, but I don’t know whether I want to act differently depending on whether the OS does it or not”. But then, Stéphane wrote over the mailing list - https://<email address hidden>/msg00970.html - that POSIX is likely to add this, so I guess we’ll have to bite the bullet and do so.

Note that many tools and file formats (e.g. in the case of archivers) will continue to not handle sub-second timestamps, and that introducing tools that do support it *will* cause inconsistency (e.g. after unarchiving, or synchronising from another machine).

Thanks for reminding about the issue.