Time::Piece regional timezone configuration via TZ environment variable

Direct answer

Time::Piece does not provide a documented way to set a timezone offset on a per‑object basis. The module relies on Perl’s built‑in localtime (via Time::Local), which obeys the process‑wide TZ environment variable. To change the zone for a specific conversion you must modify TZ globally and reload the zone database before creating the Time::Piece object.

Likely explanation vs. confirmed facts

Likely explanation: Changing ENV{TZ} alters the underlying C library’s timezone database that Perl’s localtime consults, thereby shifting the offset and abbreviation returned by Time::Piece objects.

Confirmed facts:

• Time::Piece->new (or the localtime export) calls Perl’s built‑in localtime function.
• Perl’s localtime respects $ENV{TZ} after POSIX::tzset has been invoked.
• On systems with IANA zoneinfo (most Unix‑like platforms), a value like 'America/New_York' yields the correct Eastern time offset.

Steps needed for this case

1. Ensure the system’s zoneinfo database is installed (typically present on Linux/*BSD/macOS).
2. In your Perl script, set the environment variable:

   $ENV{TZ} = 'Europe/Paris';

3. Reload the timezone data:

   POSIX::tzset();

4. Create the Time::Piece object and use it:

   my $tp = Time::Piece->new;
   print $tp->strftime('%Y-%m-%d %H:%M:%S %Z %z');

Behavior of Time::Local::timelocal when TZ changes mid‑execution

Time::Local::timelocal ultimately calls the system mktime function, which consults the current timezone setting after tzset. Therefore:

• If you modify $ENV{TZ} and then call POSIX::tzset(), subsequent timelocal calls will interpret the supplied epoch seconds using the new zone.
• On Windows, Perl’s localtime/mktime may ignore TZ and rely on the system timezone setting; verify behavior on the target Windows version.
• In multi‑threaded programs, changing TZ without proper synchronization can cause race conditions because the timezone database is process‑wide.

Missing diagnostic detail

To give a definitive recommendation about whether you need extra safeguards (e.g., per‑thread locale handling or a fallback to DateTime), please specify the operating system you are targeting (Unix‑like vs. Windows).