Data

Tools

Indexes

Applications

Experiments

Awesome

An open API service indexing awesome lists of open source software.

https://github.com/trwyant/perl-posix-strftime-behavior

POSIX::strftime() behavior change in Perl 5.39.8.
https://github.com/trwyant/perl-posix-strftime-behavior

Last synced: 3 months ago
JSON representation

POSIX::strftime() behavior change in Perl 5.39.8.

Awesome Lists containing this project

README 

        
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 `$epoch` represents 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 be `2024-05-02 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, the `isdst` element. If this is `0` (as it is by definition in the case of `gmtime()`), 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 of `gmtime()` specify a time which is during the jump to Summer time.



These tests were done under Olson zone `America/New_York`, and with the `TZ` environment variable undefined. I note that the core Perl test `ext/POSIX/t/time.t` jumps through all sorts of hoops to try to be portable among time zones. My read of this says that the steps relevant to formatting `gmtime` output are



    $ENV{TZ} = 'UTC0UTC';

    tzset(); # From the POSIX module



Doing 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 of `GMT`, `UTC`, or `UTC0` **does** cause Perl 5.39.8 to behave like previous Perls, even in the absence of the `tzset()`.



I have read through the `perldelta.pod` for Perl 5.39.8 and not found this called out as a deliberate change. A `diff -u` between the 5.39.7 and 5.39.8 versions of `POSIX.xs` finds 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()` and `sprintf()` on the output of `gmtime()`. 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 using `strftime-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 using `strftime-try --help`.



Relevant data on the macOS Perl 5.39.8 build:



    $ perl-5.39.8/perl -V

    Summary of my perl5 (revision 5 version 39 subversion 8) configuration:

       

      Platform:

        osname=darwin

        osvers=22.6.0

        archname=darwin-2level

        uname='darwin samwise.local 22.6.0 darwin kernel version 22.6.0: tue nov 7 21:48:06 pst 2023; root:xnu-8796.141.3.702.9~2release_x86_64 x86_64 '

        config_args='-Dprefix=/trw/local/perl/5.39.8 [email protected] -Uinstallusrbinperl -e -d -Dusedevel -Uversiononly'

        hint=recommended

        useposix=true

        d_sigaction=define

        useithreads=undef

        usemultiplicity=undef

        use64bitint=define

        use64bitall=define

        uselongdouble=undef

        usemymalloc=n

        default_inc_excludes_dot=define

      Compiler:

        cc='cc'

        ccflags ='-fno-common -DPERL_DARWIN -mmacosx-version-min=13.6 -DNO_THREAD_SAFE_QUERYLOCALE -DNO_POSIX_2008_LOCALE -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -I/opt/local/include'

        optimize='-O3'

        cppflags='-fno-common -DPERL_DARWIN -mmacosx-version-min=13.6 -DNO_THREAD_SAFE_QUERYLOCALE -DNO_POSIX_2008_LOCALE -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -I/opt/local/include'

        ccversion=''

        gccversion='Apple LLVM 15.0.0 (clang-1500.1.0.2.5)'

        gccosandvers=''

        intsize=4

        longsize=8

        ptrsize=8

        doublesize=8

        byteorder=12345678

        doublekind=3

        d_longlong=define

        longlongsize=8

        d_longdbl=define

        longdblsize=16

        longdblkind=3

        ivtype='long'

        ivsize=8

        nvtype='double'

        nvsize=8

        Off_t='off_t'

        lseeksize=8

        alignbytes=8

        prototype=define

      Linker and Libraries:

        ld='cc'

        ldflags =' -mmacosx-version-min=13.6 -fstack-protector-strong -L/usr/local/lib -L/opt/local/lib'

        libpth=/usr/local/lib /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/lib /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib /opt/local/lib /usr/lib

        libs=-lgdbm

        perllibs=

        libc=

        so=dylib

        useshrplib=false

        libperl=libperl.a

        gnulibc_version=''

      Dynamic Linking:

        dlsrc=dl_dlopen.xs

        dlext=bundle

        d_dlsymun=undef

        ccdlflags=' '

        cccdlflags=' '

        lddlflags=' -mmacosx-version-min=13.6 -bundle -undefined dynamic_lookup -L/usr/local/lib -L/opt/local/lib -fstack-protector-strong'



    Characteristics of this binary (from libperl): 

      Compile-time options:

        HAS_LONG_DOUBLE

        HAS_STRTOLD

        HAS_TIMES

        PERLIO_LAYERS

        PERL_COPY_ON_WRITE

        PERL_DONT_CREATE_GVSV

        PERL_HASH_FUNC_SIPHASH13

        PERL_HASH_USE_SBOX32

        PERL_MALLOC_WRAP

        PERL_OP_PARENT

        PERL_PRESERVE_IVUV

        PERL_USE_DEVEL

        PERL_USE_SAFE_PUTENV

        USE_64_BIT_ALL

        USE_64_BIT_INT

        USE_LARGE_FILES

        USE_LOCALE

        USE_LOCALE_COLLATE

        USE_LOCALE_CTYPE

        USE_LOCALE_NUMERIC

        USE_LOCALE_TIME

        USE_PERLIO

        USE_PERL_ATOF

      Built under darwin

      Compiled at Feb 24 2024 08:32:39

      @INC:

        /trw/local/perl/5.39.8/lib/site_perl/5.39.8/darwin-2level

        /trw/local/perl/5.39.8/lib/site_perl/5.39.8

        /trw/local/perl/5.39.8/lib/5.39.8/darwin-2level

        /trw/local/perl/5.39.8/lib/5.39.8