1Image::ExifTool::Shift(U3s)er Contributed Perl DocumentatIimoange::ExifTool::Shift(3)
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6 Image::ExifTool::Shift.pl - ExifTool time shifting routines
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9 This module contains routines used by ExifTool to shift date and time
10 values.
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13 Time shifts are applied to standard EXIF-formatted date/time values
14 (ie. "2005:03:14 18:55:00"). Date-only and time-only values may also
15 be shifted, and an optional timezone (ie. "-05:00") is also supported.
16 Here are some general rules and examples to explain how shift strings
17 are interpreted:
18 Date-only values are shifted using the following formats:
20 'Y:M:D' - shift date by 'Y' years, 'M' months and 'D' days
22 'M:D' - shift months and days only
23 'D' - shift specified number of days
24 Time-only values are shifted using the following formats:
26 'h:m:s' - shift time by 'h' hours, 'm' minutes and 's' seconds
28 'h:m' - shift hours and minutes only
29 'h' - shift specified number of hours
30 Timezone shifts are specified in the following formats:
32 '+h:m' - shift timezone by 'h' hours and 'm' minutes
34 '-h:m' - negative shift of timezone hours and minutes
35 '+h' - shift timezone hours only
36 '-h' - negative shift of timezone hours only
37 A valid shift value consists of one or two arguments, separated by a
39 space. If only one is provided, it is assumed to be a time shift when
40 applied to a time-only or a date/time value, or a date shift when
41 applied to a date-only value. For example:
42 '7' - shift by 1 hour if applied to a time or date/time
44 value, or by one day if applied to a date value
45 '2:0' - shift 2 hours (time, date/time), or 2 months (date)
46 '5:0:0' - shift 5 hours (time, date/time), or 5 years (date)
47 '0:0:1' - shift 1 sec (time, date/time), or 1 day (date)
48 If two arguments are given, the date shift is first, followed by the
50 time shift:
51 '3:0:0 0' - shift date by 3 years
53 '0 15:30' - shift time by 15 hours and 30 minutes
54 '1:0:0 0:0:0+5:0' - shift date by 1 year and timezone by 5 hours
55 A date shift is simply ignored if applied to a time value or visa
57 versa.
58 Numbers specified in shift fields may contain a decimal point:
60 '1.5' - 1 hour 30 minutes (time, date/time), or 1 day (date)
62 '2.5 0' - 2 days 12 hours (date/time), 12 hours (time) or
63 2 days (date)
64 And to save typing, a zero is assumed for any missing numbers:
66 '1::' - shift by 1 hour (time, date/time) or 1 year (date)
68 '26:: 0' - shift date by 26 years
69 '+:30 - shift timezone by 30 minutes
70 Below are some specific examples applied to real date and/or time val‐
72 ues ('Dir' is the applied shift direction: '+' is positive, '-' is neg‐
73 ative):
74 Original Value Shift Dir Shifted Value
76 --------------------- ------- --- ---------------------
77 '20:30:00' '5' + '01:30:00'
78 '2005:01:27' '5' + '2005:02:01'
79 '11:54:00' '2.5 0' - '23:54:00'
80 '2005:11:02' '2.5 0' - '2005:10:31'
81 '2005:11:02 11:54:00' '2.5 0' - '2005:10:30 23:54:00'
82 '2004:02:28 08:00:00' '1 1.3' + '2004:02:29 09:18:00'
83 '07:00:00' '-5' + '07:00:00'
84 '07:00:00+01:00' '-5' + '07:00:00-04:00'
85 '07:00:00Z' '+2:30' - '07:00:00-02:30'
86 '1970:01:01' '35::' + '2005:01:01'
87 '2005:01:01' '400' + '2006:02:05'
88 '10:00:00.00' '::1.33' + '09:59:58.67'
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91 The format of the original date/time value is not changed when the time
92 shift is applied. This means that the length of the date/time string
93 will not change, and only the numbers in the string will be modified.
94 The only exception to this rule is that a 'Z' timezone is changed to
95 '+00:00' notation if a timezone shift is applied. A timezone will not
96 be added to the date/time string.
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99 This module is perhaps more complicated than it needs to be because it
100 is designed to be very flexible in the way time shifts are specified
101 and applied...
102 The ability to shift dates by Y years, M months, etc, is somewhat con‐
104 tradictory to the goal of maintaining a constant shift for all time
105 values when applying a batch shift. This is because shifting by 1
106 month can be equivalent to anything from 28 to 31 days, and 1 year can
107 be 365 or 366 days, depending on the starting date.
108 The inconsistency is handled by shifting the first tag found with the
110 actual specified shift, then calculating the equivalent time difference
111 in seconds for this shift and applying this difference to subsequent
112 tags in a batch conversion. So if it works as designed, the behaviour
113 should be both intuitive and mathematically correct, and the user
114 shouldn't have to worry about details such as this (in keeping with
115 Perl's "do the right thing" philosophy).
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118 Copyright 2003-2007, Phil Harvey (phil at owl.phy.queensu.ca)
119 This library is free software; you can redistribute it and/or modify it
121 under the same terms as Perl itself.
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124 Image::ExifTool(3pm)
125perl v5.8.8 2007-09-12 Image::ExifTool::Shift(3)