jetlag.pl

#!/usr/bin/env perl
use strict;
use warnings qw(all);

use DateTime;

my $year = $ARGV[0] || DateTime->now->year;

for (
    my ($here, $there) = map {
        DateTime->new(
            year        => $year,
            month       => 1,
            day         => 1,
            hour        => 12,
            time_zone   => $_,
        )
    } qw(Europe/Amsterdam America/Sao_Paulo);
    $here->year == $year;
    $here->add(days => 1) && $there->add(days => 1)
) {
    my $delta = $there - $here;
    printf "%s\t%d\n",
        $here->dmy,
        $delta->in_units("hours");
}