How to get TZ difference?

[dda]

Hi Monks!

Is it possible to get the difference from GMT in hours? My $ENV{TZ } is not set, however, the following code shows some values:

#!/usr/bin/perl -w

use strict;
use POSIX;

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

print "std: $std\n";
print "dst: $dst\n";
print "TZ: " . ($ENV{TZ} || "Unset") . "\n";

Result is:

on Win32 machine:
 std: Russian Standard Time
 dst: Russian Daylight Time
 TZ: Unset
on linux machine:
 std: GMT
 dst: GMT
 TZ: Unset

Where does perl get those values? At he same time, php code:

<?php
$stz = date("Z");
echo $stz/60/60;
?>

shows 4..

--dda

[adrianh]

Windows boxes - no ideas.

On Un*x boxes, there are a number of files that can be used to store timezones (/etc/localtime, /etc/timezone, probably some others.)

If you're playing with timezone code I recommend you take a look at the new DateTime modules - DateTime::TimeZone in particular. Very useful stuff.

[BrowserUk]

The posix subsytem on win32 falls back to using values from the registry if the TZ environment variable isn't set.

The key in question is

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation

---

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller

[hsweet]

One way might be to use Perl's localtime and gmtime functions. Something like this should work.

$local=(localtime)[2];
$gmt=(gmtime)[2];
$diff=$gmtime-$local;  #depending on which side of the line you are on

Time flies like an arrow, fruit flies like banannas

[sgifford]

This doesn't work when localtime and gmtime are on different days (ie, in zone GMT+4 between 8:00pm and 11:59pm). Here's a fixed version:

#!/usr/bin/perl

@local=(localtime);
@gmt=(gmtime);
$diff=$gmt[2]-$local[2];
if ($gmt[5] > $local[5] || $gmt[7] > $local[7])
{
  $diff += 24;
}
elsif ($gmt[5] < $local[5] || $gmt[7] < $local[7])
{
  $diff -= 24;
}

[sgifford]

This is a little shorter and more confusing.

  @local=(localtime(time+$off_h*60*60));
  @gmt=(gmtime(time+$off_h*60*60));
  $diff=$gmt[2]-$local[2] + ($gmt[5] <=> $local[5] 
                                     || 
                             $gmt[7] <=> $local[7])*24;

[hsweet]

thanks for the correction

Time flies like an arrow, fruit flies like banannas

[Anonymous Monk]

you forgot to compare the months in case when we have last day of the month, around midnight it will return inccorect results