working with epoch seconds

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

Dear Monks

Just at the point I thought everything was working fine I noticed the following problem (see test script):

#! /usr/bin/perl -l

use strict ;
use warnings ;
use POSIX 'strftime';

my $a = time() ; # local time is now 12:35:00 


print "input time is $a" ;

print "gmtime gives: ".gmtime($a) ;

my $b = strftime("%s", gmtime(int $a)) ; # %s converts date to epoch 

print "diff is: ".($a - $b) ;
[download]

Output

  input time is   1160390100
  gmtime gives: Mon Oct  9 10:35:00 2006
  diff is: 3600
[download]

So, the 3600 is my problem, it should have been zero (I think)....
Any suggestions what I do wrong ? or how to get the the same result ($a) back ?

Thnx LuCa

ps maybe it will help, my localtime zone is CEST (there is a 2 hours diff with GMT)

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Re: working with epoch seconds by McDarren (Abbot) on Oct 09, 2006 at 11:03 UTC
There is nothing wrong with that output at all. gmtime gives you exactly what it says - GMT time. So unless you happen to be in the GMT timezone, there will always be a difference. For example, when I run your script on my local machine I get: `input time is 1160391190 gmtime gives: Mon Oct 9 10:53:10 2006 diff is: 28800` [download] My local timezone is GMT+8 hours, so the output is correct. Regards your local timezone being GMT+2, are you sure? Perhaps you are not taking something silly into account, like daylight savings? As to what you should do about that, I'm afraid that I'm a little unclear on exactly what it is that you are trying to achieve - so perhaps you need to explain that a little more. As a side note, you should try to avoid using $a and $b as variable names - they are special package global variables that are used by sort. Cheers, Darren :)	[reply] [d/l]
Re^2: working with epoch seconds by jeanluca (Deacon) on Oct 09, 2006 at 11:30 UTC
very interesting that you get 28800 (8 hours). I should have had 7200, but I get 3600. So, the output from strftime is in the localtime zone ? Any suggestions how to define the output timezone ? Thanks a lot LuCa UPDATE: This seems todo more or less what I need: `use DateTime ; my $now = DateTime->now->set_time_zone("UTC") ; print $now->strftime("%s", time()) ;` [download]	[reply] [d/l]
Re^3: working with epoch seconds by Hue-Bond (Priest) on Oct 09, 2006 at 11:47 UTC
Use a module: `use strict; use warnings; use DateTime; my $dt = DateTime->now; print $dt->strftime ("%Y %m %d, %H:%M:%S %Z\n"); $dt->set_time_zone ('America/New_York'); print $dt->strftime ("%Y %m %d, %H:%M:%S %Z\n"); __END__ 2006 10 09, 11:45:55 UTC 2006 10 09, 07:45:55 EDT` [download] Update: Ah, you figured it out. That's great :^). -- David Serrano	[reply] [d/l]
Re^4: working with epoch seconds by jeanluca (Deacon) on Oct 09, 2006 at 12:34 UTC
Re^5: working with epoch seconds by Hue-Bond (Priest) on Oct 09, 2006 at 12:58 UTC
Re: working with epoch seconds by ysth (Canon) on Oct 10, 2006 at 02:27 UTC
%s seems to be a non-portable extension; I'm not sure what it is supposed to return. If you are looking for the reverse of gmtime, try Time::Local's timegm.	[reply]