Karl Berry wrote:
Does BSD ls(1) support "--time=ctime --time-style=full-iso"?
BSD ls does not support any --longopts. Looking at the man page,
I don't see "millisecond" or "subsecond" etc. mentioned, though I could
easily be missing it. E.g.,
https://man.freebsd.org/cgi/man.cgi?ls
Even if there is such an option, I am skeptical of how portable it would
be, or trying to discern whether it is really working or not. All the
evidence so far is that it is very difficult to determine whether
subsecond mtimes are sufficiently supported or not. Speaking in general,
I don't think trying to get into system-specific behaviors, of whatever
kind, is going to help.
[*sigh*]
It seems that there is no good way for configure to read timestamps, so
we are limited to testing if file ages are distinguishable.
Still, could we use make(1) for *all* of the testing and not use `ls -t`
at all? A rough outline would be something like: (lightly tested; runs
in about 2.2s here)
8<------
# The case below depends on the 1/10 + 9/10 = 10/10 pattern.
am_try_resolutions="0.01 0.09 0.1 0.9 1"
echo '#' > conftest.mk
i=0
for am_try_res in $am_try_resolutions; do
echo ts${i} > conftest.ts${i}
sleep $am_try_res
echo "conftest.ts${i}: conftest.ts"`expr 1 + $i` >> conftest.mk
echo " echo $am_try_res" >> conftest.mk
i=`expr 1 + $i`
done
echo end > conftest.ts${i}
# This guess can be one step too fast, if the shorter delay just
# happened to span a clock tick boundary.
am_resolution_guess=`make -f conftest.mk conftest.ts0 | tail -1`
case $am_resolution_guess in
*9)
i=no
for am_try_res in $am_try_resolutions; do
if test x$i = xyes; then
am_resolution=$am_try_res
break
fi
test x$am_try_res = x$am_resolution_guess && i=yes
done
;;
*)
am_resolution=$am_resolution_guess
;;
esac
8<------
The trick is that the various options form a dependency chain, but the
command make will execute does /not/ actually touch the target, so it
stops when the files are no longer distinguishable. This distinguishes
between a tmpfs (which has nanosecond resolution here) and /home (which
is an older filesystem with only 1-second resolution). I am not sure
what it does with FAT yet. There should be some way to use 0.1+0.9+1 =
2 and 0.01+0.09+0.1+0.9+1 > 2 to check for that (accurately!) without
further sleeps.
-- Jacob
