How do I determine the current timezone a machine is set to with Perl?

Question

I had assumed it would be as simple as $ENV{TZ}, but the TZ environment variable is not set, and yet the date command still knows I am in EDT, so there must be some other way of determining timezone (other than saying chomp(my $tz = qx/date +%Z/);).

Answer 1

If you want something more portable than POSIX (but probably much slower) you can use DateTime::TimeZone for this:

use DateTime::TimeZone;

print DateTime::TimeZone->new( name => 'local' )->name();

Answer 2

use POSIX;
localtime();
my ($std, $dst) = POSIX::tzname();

tzname() gives you access to the POSIX global tzname - but you need to have called localtime() for it to be set in the first place.

Answer 3

If you just need something like +05:30 (UTC+5.5/India time), you may use the following code.

my @lt = localtime();
my @gt = gmtime();

my $hour_diff = $lt[2] - $gt[2];
my $min_diff  = $lt[1] - $gt[1];

my $total_diff = $hour_diff * 60 + $min_diff;
my $hour = int($total_diff / 60);
my $min = abs($total_diff - $hour * 60);

print sprintf("%+03d:%02d", $hour, $min);

This answer is inspired by Pavel's answer above.