http://qs321.pair.com?node_id=637449

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

I recently had to add some code that sets $ENV{TZ} to the correct local time. (Date::Manip requires this, and it wasn't already in my ENV on windows.) I've noticed that since doing that, when I call one perl script from another the localtime incorrectly returns GMT in the called script. 
$ENV{'TZ'} = '-0400';  # also tried 'US/Eastern' with same result.

print qq{---- $ENV{'COUNT'} ----
TZ: $ENV{'TZ'}
localtime: } . scalar(localtime) . "\n";

$ENV{'COUNT'}++;
exit if $ENV{'COUNT'} > 3;

system("C:\\perl\\bin\\perl.exe C:\\cgi\\test");

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The result is: 
C:\FootPrints1\cgi>C:\perl\bin\perl.exe C:\cgi\test
----  ----
TZ: -0400
localtime: Thu Sep  6 10:46:07 2007
---- 1 ----
TZ: -0400
localtime: Thu Sep  6 14:46:07 2007
---- 2 ----
TZ: -0400
localtime: Thu Sep  6 14:46:07 2007
---- 3 ----
TZ: -0400
localtime: Thu Sep  6 14:46:07 2007

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I'm using ActiveState 5.8.8. When I try the same on Solaris with 5.8.1 it always shows the correct local time. I tried the following code after setting ENV{TZ}, but it had no effect on the result: 
use POSIX();
POSIX::tzset();

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Any ideas how I can make localtime give me the local time (while still setting ENV{TZ} to keep Date::Manip happy)? What settings does localtime depend on?

Thanks, Joe

Replies are listed 'Best First'.
Re: ENV{TZ} and localtime? (inconsistent time in child script)
by ikegami (Patriarch) on Sep 06, 2007 at 16:54 UTC

    I started looking into this, but I hit the limit of my currently available resources. I hope to look further into this tonight. Here's what I found out so far:

    • POSIX::tzset is a thin wrapper for the C library function with the same name. The entirety of the XS code is:

      void
tzset()

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    • Windows and Visual Studio support tzset.

    • Changes to %ENV are reflected in the process's actual environment. I used Win32::ExpandEnvironmentStrings (which is mapped to a system call that knows nothing of %ENV) to verify this.

    I hope to test the example code in MSDN's tzset documentation using VS6, what ActivePerl uses.

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[select]
      Thanks, I think I found an solution in the docs you referenced for _tzset: 
      Use the following syntax to set the TZ environment variable:

set TZ=tzn[+ | –]hh[:mm[:ss] ][dzn]

tzn
Three-letter time-zone name, such as PST. You must specify the correct
+ offset from local time to UTC.

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      So I tried "EST5EDT" instead of -0400, and that gives the right result. I'm still not sure why it behaves differently when called via system() though.

      update:used code tags so brackets in syntax aren't hidden.

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[d/l]
Re: ENV{TZ} and localtime? (inconsistent time in child script)
by gam3 (Curate) on Sep 06, 2007 at 15:51 UTC
    Works on linux. I assume that TZ must be being set when perl is run. One thing that you could do is run perl from a batch file and set TZ in that.
    -- gam3
    A picture is worth a thousand words, but takes 200K.
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