Excellent Monks!

Last night, as I was toiling away at one of my current Everything Engine projects, I came upon an older item in my to do list that, while at first glance appearing quite simple, has now consumed (at least the anal-retentive part of) my mind ;)

The task is this: given a date and time in GMT, I want to be able to convert that date to an arbitrary time zone, respecting daylight savings and strange (i.e. not simply +1 or -1) hour offsets, and pretty-print the result for human consumption.

The method I hit upon (that doesn't employ Date::Manip, at any rate) goes something like this:

sub format_date {
    my ($epoch, $string, $timezone) = @_;

    local %ENV;
    $ENV{TZ} = $timezone || 'GMT';

    return strftime($string, localtime($epoch));
}

[download]

This works, for the most part, and plays nicely with Time::ZoneInfo. However! POSIX::strftime's %Z and %z tokens are sometimes wrong. For instance, given a date during daylight savings and one during winter time, %Z is replaced with the standard time abbreviation (i.e. for America/Chicago %Z renders CST for both dates, which would be correct for America/Regina) and %z with only the standard time offset.

Time::CTime::strftime, meanwhile, simply regurgitates the value of %ENV{TZ}.

Is there a better way to be going about these date calculations? Ideally, I'd like to be able to display EST/EDT, NZST/NZDT, etc. just like date(1) ... one way would be to gut the zoneinfo files manually for their innards, another to build a table of EST -> EDT conversions... however, the first seems not incredibly efficient while the later seems incredibly kludgy.

Any suggestions, or fine rants about time ;), would be appreciated.

baphomet.

Update: Well, it looks like I neglected to notice Class::Date. Using the to_tz() method, you get results similar to what I've used above, except that Class::Date objects keep some better information about the date's time zone. For instance,

sub format_date {

    my ($isodate, $string, $timezone) = @_;

    my $gmtdate = Class::Date->new($isodate, 'GMT');
    my $tzdate = $gmtdate->to_tz($timezone);

    return $tzdate->strftime($string);
}

[download]

will return proper results for strftime's %Z. You can also access $tzdate->tz_offset to grab GMT offset, $tzdate->tz to grab the base timezone and $tzdate->tzdst to grab the "real" timezone accounting for DST as best as zoneinfo can.

In reply to Playing with time (or, a lament to POSIX::strftime's %Z) by baphomet

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