jkeenan
commented
8 months ago POSIX::strftime() behavior change in Perl 5.39.8.
I have observed a behavior change in
POSIX::strftime()in Perl 5.39.8. This is most succinctly demonstrated by this code:say strftime '%Y-%m-%d %H:%M:%S', gmtime $epoch;If the
$epochrepresents a time when the local zone is shifted to Summer time, the output will be an hour later than the actual time. That is, at 2024-05-01 23:30:00 the output will be2024-05-02 00:30:00.Perls before 5.39.8 do not exhibit this behavior.
Using this program:
$ cat gh-22062-gmtime.pl
#!/usr/bin/env perl
use 5.14.0;
use warnings;
use Time::Local ( qw| timegm_posix | );
use POSIX ( qw| strftime | );
my $string = strftime '%Y-%m-%d %H:%M:%S',
gmtime timegm_posix( 0, 30, 23, 14, 7-1, 2023-1900 );
say $string;
my ($day_of_month) = $string =~ m/^\d{4}-\d{1,2}-(\d{1,2})/;
die "ANOMALY" unless $day_of_month == 14;... bisection with this invocation:
perl Porting/bisect.pl \
--start=v5.39.7 \
--end=v5.39.8 \
-- ./perl -Ilib /tmp/gh-22062-gmtime.pl... pointed to 36e41d53ff
36e41d53ff6a5995c16234f8027ef34b5e6a34cc is the first bad commit
commit 36e41d53ff6a5995c16234f8027ef34b5e6a34cc
Author: Karl Williamson <khw@cpan.org>
Date: Wed Jan 10 11:30:11 2024 -0700
Commit: Karl Williamson <khw@cpan.org>
CommitDate: Wed Feb 7 10:59:05 2024 -0700
Don't use both mini_mktime() and mkttime()@khwilliamson, can you take a look? Thanks.
khwilliamson
trwyant
Grinnz
tonycoz
haarg
rra
iabyn
POSIX::strftime() behavior change in Perl 5.39.8.
I have observed a behavior change in
POSIX::strftime()in Perl 5.39.8. This is most succinctly demonstrated by this code:If the
$epochrepresents a time when the local zone is shifted to Summer time, the output will be an hour later than the actual time. That is, at 2024-05-01 23:30:00 the output will be2024-05-02 00:30:00.Perls before 5.39.8 do not exhibit this behavior.
The behavior seems to be related to the value of element
[8]of the returned array, theisdstelement. If this is0(as it is by definition in the case ofgmtime()), the behavior under Perl 5.39.8 is as described in the previous paragraph. If this element is absent or-1, the output is an hour later only if the results ofgmtime()specify a time which is during the jump to Summer time.These tests were done under Olson zone
America/New_York, and with theTZenvironment variable undefined. I note that the core Perl testext/POSIX/t/time.tjumps through all sorts of hoops to try to be portable among time zones. My read of this says that the steps relevant to formattinggmtimeoutput areDoing these does not affect the behavior of the code under any combination of OS and Perl I have tried. But setting
$ENV{TZ}to any one ofGMT,UTC, orUTC0does cause Perl 5.39.8 to behave like previous Perls, even in the absence of thetzset().I have read through the
perldelta.podfor Perl 5.39.8 and not found this called out as a deliberate change. Adiff -ubetween the 5.39.7 and 5.39.8 versions ofPOSIX.xsfinds two changes, but it is not obvious to me that either is relevant.In addition to this document, this Git repository contains two Perl scripts:
strftime-year
This script takes a year on the command line (defaulting to 2024), and formats the date and time for every 30 minutes throughout the year using both
strftime()andsprintf()on the output ofgmtime(). If it detects intervals when the output of the two are not the same, it reports the first time where the difference occurs, and the first time where there ceases to be a difference. You can get more information usingstrftime-year --help.strftime-try
This script formats its command-line arguments using
strftime()and prints the results. The arguments are used verbatim. You can get more information usingstrftime-try --help.Relevant data on the macOS Perl 5.39.8 build: