174 lines
7.1 KiB
HTML
174 lines
7.1 KiB
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<?xml version="1.0" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>ExifTool Date/Time Shift Module</title>
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<meta http-equiv="content-type" content="text/html; charset=utf-8" />
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<link rev="made" href="mailto:_securityagent@gamma.local" />
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</head>
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<body style="background-color: white">
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<table border="0" width="100%" cellspacing="0" cellpadding="3">
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<tr><td class="block" style="background-color: #cccccc" valign="middle">
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<big><strong><span class="block"> ExifTool Date/Time Shift Module</span></strong></big>
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</td></tr>
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</table>
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<!-- INDEX BEGIN -->
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<div name="index">
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<p><a name="__index__"></a></p>
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<ul>
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<li><a href="#name">NAME</a></li>
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<li><a href="#description">DESCRIPTION</a></li>
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<li><a href="#details">DETAILS</a></li>
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<li><a href="#notes">NOTES</a></li>
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<li><a href="#tricky">TRICKY</a></li>
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<li><a href="#bugs">BUGS</a></li>
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<li><a href="#author">AUTHOR</a></li>
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<li><a href="#see_also">SEE ALSO</a></li>
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</ul>
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<hr name="index" />
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</div>
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<!-- INDEX END -->
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<p>
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</p>
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<h1><a name="name">NAME</a></h1>
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<p>Image::ExifTool::Shift.pl - ExifTool time shifting routines</p>
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<p>
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</p>
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<hr />
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<h1><a name="description">DESCRIPTION</a></h1>
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<p>This module contains routines used by ExifTool to shift date and time
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values.</p>
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<p>
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</p>
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<hr />
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<h1><a name="details">DETAILS</a></h1>
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<p>Time shifts are applied to standard EXIF-formatted date/time values (eg.
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<code>2005:03:14 18:55:00</code>). Date-only and time-only values may also be
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shifted, and an optional timezone (eg. <code>-05:00</code>) is also supported. Here
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are some general rules and examples to explain how shift strings are
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interpreted:</p>
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<p>Date-only values are shifted using the following formats:</p>
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<pre>
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'Y:M:D' - shift date by 'Y' years, 'M' months and 'D' days
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'M:D' - shift months and days only
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'D' - shift specified number of days</pre>
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<p>Time-only values are shifted using the following formats:</p>
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<pre>
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'h:m:s' - shift time by 'h' hours, 'm' minutes and 's' seconds
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'h:m' - shift hours and minutes only
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'h' - shift specified number of hours</pre>
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<p>Timezone shifts are specified in the following formats:</p>
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<pre>
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'+h:m' - shift timezone by 'h' hours and 'm' minutes
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'-h:m' - negative shift of timezone hours and minutes
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'+h' - shift timezone hours only
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'-h' - negative shift of timezone hours only</pre>
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<p>A valid shift value consists of one or two arguments, separated by a space.
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If only one is provided, it is assumed to be a time shift when applied to a
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time-only or a date/time value, or a date shift when applied to a date-only
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value. For example:</p>
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<pre>
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'1' - shift by 1 hour if applied to a time or date/time
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value, or by one day if applied to a date value
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'2:0' - shift 2 hours (time, date/time), or 2 months (date)
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'5:0:0' - shift 5 hours (time, date/time), or 5 years (date)
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'0:0:1' - shift 1 s (time, date/time), or 1 day (date)</pre>
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<p>If two arguments are given, the date shift is first, followed by the time
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shift:</p>
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<pre>
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'3:0:0 0' - shift date by 3 years
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'0 15:30' - shift time by 15 hours and 30 minutes
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'1:0:0 0:0:0+5:0' - shift date by 1 year and timezone by 5 hours</pre>
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<p>A date shift is simply ignored if applied to a time value or visa versa.</p>
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<p>Numbers specified in shift fields may contain a decimal point:</p>
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<pre>
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'1.5' - 1 hour 30 minutes (time, date/time), or 1 day (date)
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'2.5 0' - 2 days 12 hours (date/time), 12 hours (time) or
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2 days (date)</pre>
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<p>And to save typing, a zero is assumed for any missing numbers:</p>
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<pre>
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'1::' - shift by 1 hour (time, date/time) or 1 year (date)
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'26:: 0' - shift date by 26 years
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'+:30 - shift timezone by 30 minutes</pre>
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<p>Below are some specific examples applied to real date and/or time values
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('Dir' is the applied shift direction: '+' is positive, '-' is negative):</p>
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<pre>
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Original Value Shift Dir Shifted Value
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--------------------- ------- --- ---------------------
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'20:30:00' '5' + '01:30:00'
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'2005:01:27' '5' + '2005:02:01'
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'2005:01:27 20:30:00' '5' + '2005:01:28 01:30:00'
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'11:54:00' '2.5 0' - '23:54:00'
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'2005:11:02' '2.5 0' - '2005:10:31'
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'2005:11:02 11:54:00' '2.5 0' - '2005:10:30 23:54:00'
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'2004:02:28 08:00:00' '1 1.3' + '2004:02:29 09:18:00'
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'07:00:00' '-5' + '07:00:00'
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'07:00:00+01:00' '-5' + '07:00:00-04:00'
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'07:00:00Z' '+2:30' - '07:00:00-02:30'
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'1970:01:01' '35::' + '2005:01:01'
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'2005:01:01' '400' + '2006:02:05'
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'10:00:00.00' '::1.33' - '09:59:58.67'</pre>
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<p>
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</p>
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<hr />
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<h1><a name="notes">NOTES</a></h1>
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<p>The format of the original date/time value is not changed when the time
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shift is applied. This means that the length of the date/time string will
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not change, and only the numbers in the string will be modified. The only
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exception to this rule is that a 'Z' timezone is changed to '+00:00'
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notation if a timezone shift is applied. A timezone will not be added to
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the date/time string.</p>
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<p>
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</p>
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<hr />
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<h1><a name="tricky">TRICKY</a></h1>
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<p>This module is perhaps more complicated than it needs to be because it is
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designed to be very flexible in the way time shifts are specified and
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applied...</p>
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<p>The ability to shift dates by Y years, M months, etc, conflicts with the
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design goal of maintaining a constant shift for all time values when
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applying a batch shift. This is because shifting by 1 month can be
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equivalent to anything from 28 to 31 days, and 1 year can be 365 or 366
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days, depending on the starting date.</p>
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<p>The inconsistency is handled by shifting the first tag found with the actual
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specified shift, then calculating the equivalent time difference in seconds
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for this shift and applying this difference to subsequent tags in a batch
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conversion. So if it works as designed, the behaviour should be both
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intuitive and mathematically correct, and the user shouldn't have to worry
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about details such as this (in keeping with Perl's "do the right thing"
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philosophy).</p>
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<p>
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</p>
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<hr />
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<h1><a name="bugs">BUGS</a></h1>
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<p>Due to the use of the standard time library functions, dates are typically
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limited to the range 1970 to 2038 on 32-bit systems.</p>
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<p>
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</p>
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<hr />
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<h1><a name="author">AUTHOR</a></h1>
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<p>Copyright 2003-2016, Phil Harvey (phil at owl.phy.queensu.ca)</p>
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<p>This library is free software; you can redistribute it and/or modify it
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under the same terms as Perl itself.</p>
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<p>
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</p>
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<hr />
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<h1><a name="see_also">SEE ALSO</a></h1>
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<p><a href="ExifTool.html">Image::ExifTool(3pm)</a></p>
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<table border="0" width="100%" cellspacing="0" cellpadding="3">
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<tr><td class="block" style="background-color: #cccccc" valign="middle">
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|
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<big><strong><span class="block"> ExifTool Date/Time Shift Module</span></strong></big>
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</td></tr>
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</table>
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</body>
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</html>
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