dda has asked for the wisdom of the Perl Monks concerning the following question:

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";

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

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Where does perl get those values? At he same time, php code: 
<?php
$stz = date("Z");
echo $stz/60/60;
?>

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shows 4..

--dda

Replies are listed 'Best First'.
Re: How to get TZ difference?
by adrianh (Chancellor) on Jun 28, 2003 at 10:50 UTC

    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.

[reply]
Re: How to get TZ difference?
by BrowserUk (Patriarch) on Jun 28, 2003 at 14:09 UTC

    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


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[d/l]
Re: How to get TZ difference?
by hsweet (Pilgrim) on Jun 28, 2003 at 12:04 UTC
    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

    [download]

    Time flies like an arrow, fruit flies like banannas

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[d/l]
      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;
}

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[reply]
[d/l]
        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;

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[reply]
[d/l]
        thanks for the correction

        Time flies like an arrow, fruit flies like banannas

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

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