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ENV{TZ} and localtime? (inconsistent time in child script)

by blahblahblah (Priest)
on Sep 06, 2007 at 15:11 UTC ( #637449=perlquestion: print w/replies, xml ) Need Help??

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");
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
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();
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

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Re: ENV{TZ} and localtime? (inconsistent time in child script)
by ikegami (Pope) 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()
    • 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.

      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.
      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.

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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