Hi,
Andreas Kusalananda wrote on Sun, Jan 05, 2020 at 02:44:04PM +0100:
> The command
>
> find . -type f -mtime +0
>
> should find regular files in or below the current directory
> that were last modified strictly more than 0 day ago (i.e. 1
> day ago or more).
My first reaction was:
No, it should not. Our manual page says:
-mtime n
True if the difference between the file last modification time
and the time find was started, rounded up to the next full
24-hour period, is n 24-hour periods.
[...]
All primaries which take a numeric argument allow the number to be
preceded by a plus sign ('+') or a minus sign ('-'). A preceding plus
sign means "more than n", ...
Note the "rounded up". So what +0 tests is ceil(t/24h) > 0,
which is equivalent to t > 0, i.e. that the file was last changed
in the past (and not in the future).
If you want to find files last changed more than 1 day (24h) ago,
you have to say -mtime +1.
But note that the POSIX standard
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html
contradicts itself:
In the descriptions, wherever n is used as a primary argument,
it shall be interpreted as a decimal integer optionally preceded
by a <plus-sign> ( '+' ) or <hyphen-minus> ( '-' ), as follows:
+n More than n.
[...]
-mtime n
The primary shall evaluate as true if the file modification time
subtracted from the initialization time, divided by 86400 (with
any remainder discarded), is n.
[...]
For example, -atime 2 is true if the file was accessed any time
in the period from 72 hours to 48 hours ago.
[...]
The following command:
find / \( -name tmp -o -name '*.xx' \) -atime +7 -exec rm {} \;
removes all files named tmp or ending in .xx that have not been
accessed for seven or more 24-hour periods.
Then again, changing the last line from "seven or more" to "more
than seven" makes the POSIX description consistent, and makes it
disagree with our description and implementation because POSIX
says "remainder discarded" and we say "rounded up".
So, should we delete the "+ SECSPERDAY - 1" from f_?time() to
agree with POSIX? That might be somewhat disruptive because
it suddenly shifts the meaning of -{a,c,m}time in people's scripts
by 24 hours. It is quite likely circumstances exist where such
a shift can cause havoc in sysadmin scripts and the like.
Then again, disagreeing with POSIX (assuming that the main POSIX
text is what they mean and just the example in POSIX is wrong)
is quite ugly, too...
FreeBSD and NetBSD both have the same "rounded up" language in the
manual page and the same "+ SECSPERDAY - 1" in the -mtime
implementation, which appears to contradict the claim "The description
is also different in terms of the exact timeframe for the n case
(versus the +n or -n), but it matches all known historical
implementations" in the POSIX RATIONALE.
Is this really the mess it seems to me now, with all BSDs consistently
disagreeing with POSIX? I really hope i'm missing something here...
If people here agree that BSD and POSIX contradict each other,
should i ask about that on the Austin Group mailing list?
Yours,
Ingo
