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POMinGW MSYS, MSVCRT, and the TZ environment variable
 

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    <p>In short, how to make both MSVCRT and MinGW MSYS share the TZ environment variable without conflicts? Or, how to make both support timezones without conflicts?</p> <h2>Further information</h2> <p>In order to have date command of MSYS displaying correct local time, and because MSYS itself uses its own C runtime instead of MSVCRT, I have set TZ environment variable <a href="http://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html" rel="nofollow noreferrer">according to GNU C library documentation</a>:</p> <pre><code>export TZ="BRT+3BRST,M10.3.0/0,M2.3.0/0" </code></pre> <p>Unfortunately, <a href="http://msdn.microsoft.com/en-us/library/90s5c885%28v=vs.80%29.aspx" rel="nofollow noreferrer">this conflicts with Microsoft C runtime specs</a>, which dictates for the DST name part:</p> <blockquote> <p><em>If daylight saving time is never in effect in the locality, set TZ without a value for dzn. The C run-time library assumes the United States' rules for implementing the calculation of daylight saving time (DST)</em></p> </blockquote> <p>Hence, the simple presence of a DST name in TZ variable will cause programs relying on <code>_tzset</code> to malfunction outside the USA. This is my case with Bazaar DVCS, where I have been getting wrong commit times, one hour late, because MSVCRT assumes I have already entered DST period based on TZ setting. If I leave TZ empty, MSYS date displays UTC time, but MSVCRT (and Bazaar) works just fine. If I set TZ as above, then MSVCRT adds one hour to commit times, but MSYS date displays local time.</p> <p>Bazaar is affected because it uses Python which in turn uses MSVCRT under Windows. Even though I can remove everything from DST name on, that will break date command in MSYS. I have tried several values of TZ as well. MSYS seems to lack any further timezone support than what is described above in GNU reference. Also, I wanted to avoid having TZ not set only when invoking Bazaar, or have it set only when invoking date command, but rather a more general solution.</p> <p><strong>Alternative formats and zoneinfo database</strong></p> <p>There is an alternative format for TZ, third one in GNU documentation above, but it seems to not be supported by MSYS, as stated:</p> <blockquote> <p><em>But the POSIX.1 standard only specifies the details of the first two formats,</em></p> </blockquote> <p>It seems this third format is just IANA's Time Zone Database, <a href="http://www.iana.org/time-zones/repository/tz-link.html" rel="nofollow noreferrer">which describes a different format for TZ</a> which seems to not be supported by MSYS either, as stated:</p> <blockquote> <p><em>To use the database on an extended POSIX implementation set the TZ environment variable to the location's full name, e.g., <code>TZ="America/New_York"</code>.</em></p> </blockquote> <p>Desipe the above I tried to install IANA's zoneinfo manually onto MSYS without success. I'm not sure if these statements are correct and their formats aren't even recognized by MSYS, or if I just have failed to install zoneinfo data files correctly. I couldn't find a compiled version neither could I compile myself, so I just tried out the tzdata package from Ubuntu.</p> <p>Something odd to me, though, is that GNU C library documentation above stands it comes with a timezone database already (it sounds to me like zoneinfo). However as said I can't find any kind of timezone database installed anywhere in MSYS, neither I can find any mingw-get package related to timezones. I wonder if the developers simply removed it from the release. This is what the documentation says:</p> <blockquote> <p><em>The GNU C Library comes with a large database of time zone information for most regions of the world, which is maintained by a community of volunteers and put in the public domain.</em></p> </blockquote> <p>So in sum, if I could make zoneinfo or similar alternative work in MSYS, then I could abandon my current approach of setting TZ as above. I can't find, however, any good information about timezone support in MSYS.</p>
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