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.
11
13 ShiftTime
14 Shift date/time value
15 use Image::ExifTool;
17 $err = Image::ExifTool::ShiftTime($dateTime, $shift);
18 Inputs:
20 0) Date/time string in EXIF format (eg. "2016:01:30 11:45:00").
21 1) Shift string (see below) with optional leading sign for shift
23 direction.
24 2) [optional] Direction of shift (-1 or +1), or 0 or undef to use
26 the sign from the shift string.
27 3) [optional] Reference to time-shift hash -- filled in by first
29 call to ShiftTime, and used in subsequent calls to shift date/time
30 values by the same relative amount (see "TRICKY" section below).
31 or
33 0) Shift string (and $_ contains the input date/time string).
35 Return value:
37 Error string, or undef on success and the input date/time string is
38 shifted by the specified amount.
39
41 Time shifts are applied to standard EXIF-formatted date/time values
42 (eg. "2005:03:14 18:55:00"). Date-only and time-only values may also
43 be shifted, and an optional timezone (eg. "-05:00") is also supported.
44 Here are some general rules and examples to explain how shift strings
45 are interpreted:
46 Date-only values are shifted using the following formats:
48 'Y:M:D' - shift date by 'Y' years, 'M' months and 'D' days
50 'M:D' - shift months and days only
51 'D' - shift specified number of days
52 Time-only values are shifted using the following formats:
54 'h:m:s' - shift time by 'h' hours, 'm' minutes and 's' seconds
56 'h:m' - shift hours and minutes only
57 'h' - shift specified number of hours
58 Timezone shifts are specified in the following formats:
60 '+h:m' - shift timezone by 'h' hours and 'm' minutes
62 '-h:m' - negative shift of timezone hours and minutes
63 '+h' - shift timezone hours only
64 '-h' - negative shift of timezone hours only
65 A valid shift value consists of one or two arguments, separated by a
67 space. If only one is provided, it is assumed to be a time shift when
68 applied to a time-only or a date/time value, or a date shift when
69 applied to a date-only value. For example:
70 '1' - shift by 1 hour if applied to a time or date/time
72 value, or by one day if applied to a date value
73 '2:0' - shift 2 hours (time, date/time), or 2 months (date)
74 '5:0:0' - shift 5 hours (time, date/time), or 5 years (date)
75 '0:0:1' - shift 1 s (time, date/time), or 1 day (date)
76 If two arguments are given, the date shift is first, followed by the
78 time shift:
79 '3:0:0 0' - shift date by 3 years
81 '0 15:30' - shift time by 15 hours and 30 minutes
82 '1:0:0 0:0:0+5:0' - shift date by 1 year and timezone by 5 hours
83 A date shift is simply ignored if applied to a time value or visa
85 versa.
86 Numbers specified in shift fields may contain a decimal point:
88 '1.5' - 1 hour 30 minutes (time, date/time), or 1 day (date)
90 '2.5 0' - 2 days 12 hours (date/time), 12 hours (time) or
91 2 days (date)
92 And to save typing, a zero is assumed for any missing numbers:
94 '1::' - shift by 1 hour (time, date/time) or 1 year (date)
96 '26:: 0' - shift date by 26 years
97 '+:30' - shift timezone by 30 minutes
98 Below are some specific examples applied to real date and/or time
100 values ('Dir' is the applied shift direction: '+' is positive, '-' is
101 negative):
102 Original Value Shift Dir Shifted Value
104 --------------------- ------- --- ---------------------
105 '20:30:00' '5' + '01:30:00'
106 '2005:01:27' '5' + '2005:02:01'
107 '2005:01:27 20:30:00' '5' + '2005:01:28 01:30:00'
108 '11:54:00' '2.5 0' - '23:54:00'
109 '2005:11:02' '2.5 0' - '2005:10:31'
110 '2005:11:02 11:54:00' '2.5 0' - '2005:10:30 23:54:00'
111 '2004:02:28 08:00:00' '1 1.3' + '2004:02:29 09:18:00'
112 '07:00:00' '-5' + '07:00:00'
113 '07:00:00+01:00' '-5' + '07:00:00-04:00'
114 '07:00:00Z' '+2:30' - '07:00:00-02:30'
115 '1970:01:01' '35::' + '2005:01:01'
116 '2005:01:01' '400' + '2006:02:05'
117 '10:00:00.00' '::1.33' - '09:59:58.67'
118
120 The format of the original date/time value is not changed when the time
121 shift is applied. This means that the length of the date/time string
122 will not change, and only the numbers in the string will be modified.
123 The only exception to this rule is that a 'Z' timezone is changed to
124 '+00:00' notation if a timezone shift is applied. A timezone will not
125 be added to the date/time string.
126
128 This module is perhaps more complicated than it needs to be because it
129 is designed to be very flexible in the way time shifts are specified
130 and applied...
131 The ability to shift dates by Y years, M months, etc, conflicts with
133 the design goal of maintaining a constant shift for all time values
134 when applying a batch shift. This is because shifting by 1 month can
135 be equivalent to anything from 28 to 31 days, and 1 year can be 365 or
136 366 days, depending on the starting date.
137 The inconsistency is handled by shifting the first tag found with the
139 actual specified shift, then calculating the equivalent time difference
140 in seconds for this shift and applying this difference to subsequent
141 tags in a batch conversion. So if it works as designed, the behaviour
142 should be both intuitive and mathematically correct, and the user
143 shouldn't have to worry about details such as this (in keeping with
144 Perl's "do the right thing" philosophy).
145
147 Due to the use of the standard time library functions, dates are
148 typically limited to the range 1970 to 2038 on 32-bit systems.
149
151 Copyright 2003-2023, Phil Harvey (philharvey66 at gmail.com)
152 This library is free software; you can redistribute it and/or modify it
154 under the same terms as Perl itself.
155
157 Image::ExifTool(3pm)
158perl v5.38.0 2023-11-21 Image::ExifTool::Shift(3)