#!/usr/bin/perl

for my $tz (qw[GMT America/Chicago Europe/London]) {
    local $ENV{TZ} = $tz;
    print "$tz: " . localtime '1226667500', "\n";
}

__END__
GMT: Fri Nov 14 12:58:20 2008
America/Chicago: Fri Nov 14 06:58:20 2008
Europe/London: Fri Nov 14 12:58:20 2008