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Operating Systems Linux Ubuntu How can I find my current Daylight Saving offset? Post 302201950 by alexandicity on Tuesday 3rd of June 2008 01:07:17 PM
Old 06-03-2008
How can I find my current Daylight Saving offset?

Hello all,

I'm having a problem where a script needs to calculate GMT time given local time. For 6 months, that's easy. The other 6 months, it's not, as I have to add an extra hour to allow for Daylight Saving. At the moment, I manually add and remove an offset but, for obvious reasons, I'd prefer to automate this.

I was surprised that I couldn't find much discussion on this. What I'm looking for is some way to determine what the current local offset from GMT is. There is talk of an environment variable, $TZ, that includes information on the application of the summer time shift, but I cannot see this variable anywhere on my RHEL or Ubuntu machines.

So, is there a nice easy way to work out my current offset and therefore modify the size of the GMT shift I need. I'm thinking of using a cron, triggered at 0400 six months a year, to create $TZ or similar, but that would be ugly and just plain wrong for up to a day if I need to reboot during the summer!

Thanks!
 

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GMMKTIME(3)								 1							       GMMKTIME(3)

gmmktime - Get Unix timestamp for a GMT date

SYNOPSIS
int gmmktime ([int $hour = gmdate("H")], [int $minute = gmdate("i")], [int $second = gmdate("s")], [int $month = gmdate("n")], [int $day = gmdate("j")], [int $year = gmdate("Y")], [int $is_dst = -1]) DESCRIPTION
Identical to mktime(3) except the passed parameters represents a GMT date. gmmktime(3) internally uses mktime(3) so only times valid in derived local time can be used. Like mktime(3), arguments may be left out in order from right to left, with any omitted arguments being set to the current corresponding GMT value. PARAMETERS
o $hour - The number of the hour relative to the start of the day determined by $month, $day and $year. Negative values reference the hour before midnight of the day in question. Values greater than 23 reference the appropriate hour in the following day(s). o $minute - The number of the minute relative to the start of the $hour. Negative values reference the minute in the previous hour. Values greater than 59 reference the appropriate minute in the following hour(s). o $second - The number of seconds relative to the start of the $minute. Negative values reference the second in the previous minute. Values greater than 59 reference the appropriate second in the following minute(s). o $month - The number of the month relative to the end of the previous year. Values 1 to 12 reference the normal calendar months of the year in question. Values less than 1 (including negative values) reference the months in the previous year in reverse order, so 0 is December, -1 is November, etc. Values greater than 12 reference the appropriate month in the following year(s). o $day - The number of the day relative to the end of the previous month. Values 1 to 28, 29, 30 or 31 (depending upon the month) refer- ence the normal days in the relevant month. Values less than 1 (including negative values) reference the days in the previous month, so 0 is the last day of the previous month, -1 is the day before that, etc. Values greater than the number of days in the relevant month reference the appropriate day in the following month(s). o $year - The year o $is_dst - Parameters always represent a GMT date so $is_dst doesn't influence the result. Note This parameter has been removed in PHP 7.0.0. RETURN VALUES
Returns a integer Unix timestamp. CHANGELOG
+--------+---------------------------------------------------+ |Version | | | | | | | Description | | | | +--------+---------------------------------------------------+ | 7.0.0 | | | | | | | $is_dst parameter has been removed. | | | | | 5.1.0 | | | | | | | As of PHP 5.1.0, the $is_dst parameter became | | | deprecated. As a result, the new timezone han- | | | dling features should be used instead. | | | | +--------+---------------------------------------------------+ EXAMPLES
Example #1 gmmktime(3) basic example <?php // Prints: July 1, 2000 is on a Saturday echo "July 1, 2000 is on a " . date("l", gmmktime(0, 0, 0, 7, 1, 2000)); ?> SEE ALSO
mktime(3), date(3), time(3). PHP Documentation Group GMMKTIME(3)
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