How can I change the timezone of a datetime value in Perl?

Question

Using this function:

perl -e 'use Time::Local; print timelocal("00","00","00","01","01","2000"),"\n";'

It will return an epochtime - but only in GMT - if i want the result in GMT+1 (which is the systems localtime(TZ)), what do i need to change?

Thanks in advance,

Anders

Answer 1

There is only one standard definition for epochtime, based on UTC, and not different epochtimes for different timezones.

If you want to find the offset between gmtime and localtime, use

use Time::Local;
@t = localtime(time);
$gmt_offset_in_seconds = timegm(@t) - timelocal(@t);

Answer 2

use DateTime;
my $dt   = DateTime->now;
$dt->set_time_zone( 'Europe/Madrid' );

Answer 3

While Time::Local is a reasonable solution, you may be better off using the more modern DateTime object oriented module. Here's an example:

use strict;
use DateTime;
my $dt = DateTime->now;
print $dt->epoch, "\n";

For the timezones, you can use the DateTime::TimeZone module.

use strict;
use DateTime;
use DateTime::TimeZone;

my $dt = DateTime->now;
my $tz = DateTime::TimeZone->new(name => "local");

$dt->add(seconds => $tz->offset_for_datetime($dt));

print $dt->epoch, "\n";

CPAN Links:

DateTime

Answer 4

You just need to set the timezone. Try:

env TZ=UTC+1 perl -e 'use Time::Local; print timelocal("00","00","00","01","01","2000"),"\n";'

Answer 5

Time::Local::timelocal is the inverse of localtime. The result will be in your host's local time:

$ perl -MTime::Local -le \
    'print scalar localtime timelocal "00","00","00","01","01","2000"'
Tue Feb  1 00:00:00 2000

Do you want the gmtime that corresponds to that localtime?

$ perl -MTime::Local' -le \
    'print scalar gmtime timelocal "00","00","00","01","01","2000"'
Mon Jan 31 23:00:00 2000

Do you want it the other way around, the localtime that corresponds to that gmtime?

$ perl -MTime::Local -le \
    'print scalar localtime timegm "00","00","00","01","01","2000"'
Tue Feb  1 01:00:00 2000

Answer 6

An other example based on DateTime::Format::Strptime

use strict;
use warnings;
use v5.10;
use DateTime::Format::Strptime;

my $s = "2016-12-22T06:16:29.798Z";
my $p = DateTime::Format::Strptime->new(
  pattern => "%Y-%m-%dT%T.%NZ",
  time_zone => "UTC"
);

my $dt = $p->parse_datetime($s);    
$dt->set_time_zone("Europe/Berlin");
say join ' ', $dt->ymd, $dt->hms; # shows 2016-12-22 07:16:29