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Date::Manip::Recur(3) User Contributed Perl DocumentationDate::Manip::Recur(3)

NAME
       Date::Manip::Recur - methods for working with recurring events

SYNOPSIS
	  use Date::Manip::Recur;
	  $date = new Date::Manip::Recur;

DESCRIPTION
       This module contains functions useful in parsing and manipulating
       recurrences.  A recurrence is a notation for defining when a recurring
       event occurs.  For example, if an event occurs every other Friday or
       every 4 hours, this can be defined as a recurrence. A fully specified
       recurrence consists of the following pieces of information:

       Frequency
	   The most basic piece of information is a frequency which is the
	   description of when the event occurs.

	   Examples include:

	      the first of every month
	      every other day
	      the 4th Thursday of each month at 2:00 PM
	      every 2 hours and 30 minutes

	   All of these can be expressed as a frequency.

	   NOTE: When applying a frequency to get a list of dates on which a
	   recurring event occurs, a delta is created from the frequency which
	   is applied repeatedly to get all dates on which a recurring event
	   occurs.  The deltas will always be exact or approximate. There is
	   no support for business mode recurrences. However, with the careful
	   use of modifiers (discussed below), most recurring business events
	   can be determined too.

       Range
	   In order to actually get a list of dates on which a recurring event
	   occur, a start and end date are required for all but the most
	   trivial recurrences.

	   For example, if the frequency was

	      the first of every month

	   and the start/end dates were Jan 1 2000 and May 31 2000, you could
	   get the dates:

	      Jan 1 2000
	      Feb 1 2000
	      Mar 1 2000
	      Apr 1 2000
	      May 1 2000

       Base date
	   With most frequencies, it is necessary to have a base date (a date
	   on which the recurring event occurred) in order to determine other
	   dates when it will occur.

	   A frequency like:

	      the first of every month

	   does not require a base date, but a frequency like:

	      every other Friday

	   does. Without a base date, it's impossible to determine whether any
	   given Friday is one in which the event occurs, or one in which it
	   does not occur.

	   NOTE: For performance reasons, it is useful (but not required) for
	   the base date to occur as close to the start of the range as
	   possible. Placing the base date as the last date on which the event
	   occurs on or before the start date is ideal. The further the base
	   date is away from this date, the more intermediate calculations
	   will need to be done.

       Modifier
	   Complex recurring events may require the use of modifiers in order
	   to get them correct.

	   For example, in America, many places treat Thanksgiving and the day
	   after as holidays.

	   Thanksgiving is easy to define using the frequency:

	      4th Thursday of every November

	   but the day after is NOT possible to define only as a frequency.
	   Depending on the year, the day after the 4th Thursday may be the
	   4th or 5th Friday.

	   The day after Thanksgiving can be defined as the frequency and
	   modifier:

	      4th Thursday of every November
	      +1 day

	   Modifiers can also be used to create events that happen only on
	   business days.

       With these pieces of information, the list of dates in the range can be
       obtained where the recurring event occurs.

       NOTE: both dates in the range and the base date (if necessary) must all
       be in the same time zone, and use the same Date::Manip::Base object.

FREQUENCY NOTATION
       The syntax for specifying a frequency requires some explanation. It is
       very concise, but contains the flexibility to express every single type
       of recurring event I could think of.

       The syntax of the frequency description is a colon separated list of
       the format Y:M:W:D:H:MN:S (which stand for year, month, week, etc.).
       One (and only one) of the colons may optionally be replaced by an
       asterisk, or an asterisk may be prepended to the string.	 For example,
       the following are all valid frequency descriptions:

	 1:2:3:4:5:6:7
	 1:2*3:4:5:6:7
	*1:2:3:4:5:6:7

       But the following are NOT valid because they contain 2 or more
       asterisks:

	 1:2*3:4:5*6:7
	*1:2:3:4:5:6*7

       When an asterisk is included, the portion to the left of it is called
       the interval, and refers to a time interval between recurring events.
       For example, if the interval of the frequency is:

	 1:2*

       it means that the recurring event occurs approximately every 1 year and
       2 months.  The interval is approximate because elements to the right of
       the asterisk, as well as any modifiers included in the recurrence, will
       affect when the actual events occur.

       If no asterisks are included, then the entire recurrence is an
       interval.  For example,

	 0:0:0:1:12:0:0

       refers to an event that occurs every 1 day, 12 hours.

       The portion of the frequency that occur after an asterisk is called the
       recurrence time (or rtime), and refers to a specific value (or values)
       for that type of time element (i.e. exactly as it would appear on a
       calendar or a clock).  For example, if the frequency ends with the
       rtime:

	 *12:0:0

       then the recurring event occurs at 12:00:00 (noon).

       For example:

	 0:0:0:2*12:30:0      every 2 days at 12:30 (each day)

       Elements in the rtime can be listed as single values, ranges (2 numbers
       separated by a dash "-"), or a comma separated list of values or
       ranges.	In most cases, negative values are appropriate for the week or
       day values. -1 stands for the last possible value, -2 for the second to
       the last, etc.

       If multiple values are included in more than one field in the rtime,
       every possible combination will be used. For example, if the frequency
       ends with the rtime:

	 *12-13:0,30:0

       the event will occur at 12:00, 12:30, 13:00, and 13:30.

       Some examples are:

	 0:0:0:1*2,4,6:0:0    every day at at 02:00, 04:00, and 06:00
	 0:0:0:2*12-13:0,30:0 every other day at 12:00, 12:30, 13:00,
			      and 13:30
	 0:1:0*-1:0:0:0	      the last day of every month
	 *1990-1995:12:0:1:0:0:0
			      Dec 1 in 1990 through 1995

       There is no way to express the following with a single recurrence:

	 every day at 12:30 and 1:00

       You have to use two recurrences to do this.

       You can include negative numbers in ranges. For example, including the
       range 2--2 in the day element means to go from the 2nd day to the 2nd
       to the last day. Currently, negative values are only defined in the
       week and day fields.

       When specifying a range, the first value must be less than the second
       or else nothing will be returned.

       When both the week and day elements are non-zero and the day is right
       of the asterisk, the day refers to the day of week. The following
       examples illustrate these type of frequencies:

	 0:1*4:2:0:0:0	      4th Tuesday (day 2) of every month
	 0:1*-1:2:0:0:0	      last Tuesday of every month
	 0:0:3*2:0:0:0	      every 3rd Tuesday (every 3 weeks
			      on 2nd day of week)
	 1:0*12:2:0:0:0	      the 12th Tuesday of each year

       NOTE: The day of week refers to the numeric value of each day as
       specified by ISO 8601. In other words, day 1 is ALWAY Monday, day 7 is
       ALWAYS Sunday, etc., regardless of what day of the week the week is
       defined to begin on (using the FirstDay config variable). So when the
       day field refers to the day of week, it's value must be 1-7 (it cannot
       be a negative number), a range, or a comma separated list.

       When the week element is zero and the month element is non-zero and the
       day element is right of the asterisk, the day value is the day of the
       month (it can be from 1 to 31 or -1 to -31 counting from the end of the
       month).

	 3*1:0:2:12:0:0	      every 3 years on Jan 2 at noon
	 0:1*0:2:12,14:0:0    2nd of every month at 12:00 and 14:00
	 0:1:0*-2:0:0:0	      2nd to last day of every month

       NOTE: If the day given refers to the 29th, 30th, or 31st, in a month
       that does not have that number of days, it is ignored. For example, if
       you ask for the 31st of every month, it will return dates in Jan, Mar,
       May, Jul, etc.  Months with fewer than 31 days will be ignored.

       If both the month and week elements are zero, and the year element is
       non-zero, the day value is the day of the year (1 to 365 or 366 -- or
       the negative numbers to count backwards from the end of the year).

	 1:0:0*45:0:0:0	      45th day of every year

       Specifying a day that doesn't occur in that year silently ignores that
       year. The only result of this is that specifying +366 or -366 will
       ignore all years except leap years.

       If the week element is non-zero and to the right of the asterisk, and
       the day element is zero, the frequency refers to the first day of the
       given week of the month or week of the year:

	 0:1*2:0:0:0:0	      the first day of the 2nd week of
			      every month
	 1:0*2:0:0:0:0	      the first day of the 2nd week of
			      every year

       A set of tables describing every possible combination of Y/M/W/D
       meanings, and giving an example of each is included below in the
       section LIST OF Y/M/W/D FREQUENCY DEFINITIONS.

       NOTE: If all fields left of the asterisk are zero, the last one is
       implied to be 1. In other words, the following are equivalent:

	  0:0:0*x:x:x:x
	  0:0:1*x:x:x:x

       and can be thought of as every possible occurence of the rtime.

BASE DATES
       As mentioned above, base dates are not required for some types of
       recurrences.

       Any time a frequency refers to every single possible value as specified
       by the rtime, no base date is required.

       For example, the frequency:

	  0:0:1*1:12:0:0      every Monday at noon

       refers to every single "Monday at noon" (which is the value specified
       by the rtime).

       The frequency:

	  0:0:2*1:12:0:0      every other Monday at noon

       does not, so a base date is required.

       The general rule is that if an interval consists of zeros followed by a
       single one (i.e. 0:0:1), no base date is required.

       A recurrence of the form *Y:M:W:D:H:MN:S also does not use a base date.

       The base date is used to provide the bare minimum information. For
       example, the recurrence:

	  0:0:3*4:0:0:0	      every 3 weeks on Thursday

       requires a base date to determine the week, but nothing else. Using the
       standard definition (Monday-Sunday) for a week, and given that one week
       in August 2009 is Aug 10 to Aug 16, any date in the range Aug 10 to Aug
       16 will give the same results.

       Likewise, the recurrence:

	 1:3*0:4:0:0:0	      every 1 year, 3 months on the 4th
			      day of the month

       would only use the year and month of the base date, so all dates in a
       given month would give the same set of recurring dates.

       If a base date is specified for a recurrence which does not require it,
       it will be completely ignored.

       A default base date is not supplied when a recurrence is created.

DATE RANGE
       The start and end dates form the range in which recurring events can
       fall into.

       Every recurring date will fall in the limit:

	  start <= date <= end

       When a recurrence is created, it may include a default range, and this
       is handled by the RecurRange config variable.

OTHER FREQUENCY FORMATS
       There are a small handful of English strings (or the equivalent in
       other languages) which can be parsed in place of a numerical frequency.
       These include:

	 every Tuesday in June [1997]
	 2nd Tuesday in June [1997]
	 last Tuesday in June [1997]

	 every Tuesday of every month [in 1997]
	 2nd Tuesday of every month [in 1997]
	 last Tuesday of every month [in 1997]

	 every day of every month [in 1997]
	 2nd day of every month [in 1997]
	 last day of every month [in 1997]

	 every day [in 1997]
	 every 2nd day [in 1977]
	 every 2 days [in 1977]

       Each of these set the frequency. If the year is include in the string,
       it also sets the dates in the range to be the first and last day of the
       year.

       In each of these, the numerical part (i.e. 2nd in all of the examples
       above) can be any number from 1 to 31. To make a frequency with a
       larger number than that, you have to use the standard format discussed
       above.

MODIFIERS
       The following modifiers can be used (all of which are case
       insensitive).

	 PDn   : n is 1-7.  Means the previous day n not counting
			    today
	 PTn   : n is 1-7.  Means the previous day n counting today
	 NDn   : n is 1-7.  Means the next day n not counting today
	 NTn   : n is 1-7.  Means the next day n counting today

	 FDn   : n is any number.  Means step forward n days.
	 BDn   : n is any number.  Means step backward n days.
	 FWn   : n is any number.  Means step forward n workdays.
	 BWn   : n is any number.  Means step backward n workdays.

	 CWD   : the closest work day (using the TomorrowFirst
		 config variable).
	 CWN   : the closest work day (looking forward first).
	 CWP   : the closest work day (looking backward first).

		 The CWD. CWM. amd CWP will always change the
		 date to the closest work day NOT counting
		 today.

	 NWD   : next work day counting today
	 PWD   : previous work day counting today
	 DWD   : closest work day (using the TomorrowFirst config
		 variable) counting today

		 The NWD, PWD, and DWD flags all leave the date
		 unchanged if it is a work day.

	 EASTER: select easter for this year.

       CWD, CWN, and CWP will usually return the same value, but if you are
       starting at the middle day of a 3-day weekend (for example), it will
       return either the first work day of the following week, or the last
       work day of the previous week depending on whether it looks forward or
       backward first.

       All business day modifiers ignored the time, so if a date is initially
       calculated at Saturday at noon, and the FW1 is applied, the date is
       initially moved to the following Monday (assuming it is a work day) and
       the FW1 moves it to Tuesday. The final result will be Tuesday at noon.

       There is a practical limitation on how the list of dates are
       calculated.

       When calculating a list of dates, the first thing is to use the
       interval to get a list if dates. The rtime and modifiers are then
       applied to this list, and the final list is compared to the start and
       end dates, and those dates within this range are returned.

       Because dates near the edge of the range may (based on the rtime and
       modifiers) move outside the range, and dates just outside the range may
       move into the range, dates outside the range have to be added to the
       initial list. As a result, when modifiers are present, the first thing
       to do is to expand the initial range to include all dates which will
       fall inside the actual range (as specified by the begin/end date).

       So, for example, if you have begin and end dates of Jan 10 and Jan 15,
       and a modifier of FD2 (forward 2 days), then the interval will be
       applied to dates in the range Jan 7 to Jan 14. This is obtained by
       applying the FD2 modifier to get Jan 8 to Jan 13 and then adding a 1
       day fudge factor on each side to account for any changes due to the
       mtime.

       The only problem is when applying business day modifiers. Moving
       forward 1 business day (with no holidays defined, and only using the
       standard weekend definition) may mean moving forward anywhere from 1 to
       3 days.	With holidays included, it could theoretically mean moving
       forward up to a year (i.e. if there were only 1 work day in the year,
       and all others were holidays).

       In real life, it won't ever get quite that bad, but it is not at all
       unheard of for companies to close for one or two weeks at a time. As a
       result, there is no way to know exactly how many days to adjust the
       range by to be guaranteed of getting all valid dates.

       A best guess is obtained by taking into account the length of the week
       and then applying a somewhat arbitrary fudge factor.

       For example, if the standard work week is 5 days on, 2 days off, and
       you move forward 2 business days, that could be anywhere from 2 to 5
       actual days. Finally a fudge factor is applied to make sure that the
       range includes all possible days.

       The default fudge factor is 5 days, so forward 2 business days would be
       treated as forward 2 to 10 actual days, which should be enough to get
       every possible date in real life.

       The fudge factor can be set to something other than 5 using the
       RecurNumFudgeDays config variable.  It it is set to be the total number
       of holidays in the year plus 1, it should always yield correct results,
       but at some expense.

DETERMINING DATES
       In order to get a list of dates referred to by the recurrence, the
       following steps are taken.

       A list of dates is calculated
	   Based on the interval, the base date, and the range, a list of
	   dates is calculated from the interval.

	   The list of dates initially includes all dates that fall inside the
	   range plus at least one before the range, and at least one after
	   the range.  This allows dates near the edge of the range which
	   might be pushed across the edge when the rtime values are applied,
	   or modifiers applied.

	   NOTE: if the recurrence contains no interval (i.e. is of the form
	   *Y:M:W:D:H:MN:S), no date list is determined. The dates come
	   directly from the rtime values.

       The rtime values are applied
	   All rtime values are applied to the list. Any combination of rtime
	   values which produce an invalid date are ignored.

	   For example, if the rtime values refer to the '31st of each month',
	   only any dates from the list which contain months with 31 days will
	   be used.  The others will be discarded.

       Modifiers applied
	   Next, all modifiers are applied.

       The range is tested
	   Finally, any dates that fall before or after the range are
	   discarded.

	   The resulting list of dates is returned.

	   NOTE: when the recurrence contains no interval, it is not necessary
	   to specify the range, and if it is not specified, all of the dates
	   will be returned. The range MAY be specified to return only a
	   subset of the dates if desired.

HISTORY OF THE FREQUENCY NOTATION
       I realize that the frequency notation described above looks quite
       complicated at first glance, but it is (IMO) the best notation for
       expressing recurring events in existence. I actually consider it the
       single most important contribution to date/time handling in
       Date::Manip.

       When I first decided to add recurring events to Date::Manip, I first
       came up with a list of common ways of specifying recurring events, and
       then went looking for a notation that could be used to define them.

       After looking in several specifications (including ISO 8601) and after
       a discussion on a mailing list of calendar related topics, it appeared
       like there was no concise, flexible notation for handling recurring
       events that would handle all of the common forms I'd come up with.

       So, as a matter of necessity, I set about inventing my own notation. As
       I was looking at my list, it struck me that all of the parts which
       specified a frequency were higher level (i.e. referred to a larger unit
       of time) than those parts which specified a specific value (what I've
       called the rtime). In other words, when the terms were laid out from
       year down to seconds, the frequency part was always left of specific
       values.

       That led immediately to the notation described above, so I started
       analyzing it to figure out if it could express all of the recurring
       events I'd come up with. It succeeded on 100% of them. Not only that,
       but by playing with different values (especially different combinations
       of m/w/d values), I found that it would define recurring events that I
       hadn't even thought of, but which seemed perfectly reasonable in
       hindsight.

       After a very short period, I realized just how powerful this notation
       was, and set about implementing it, and as I said above, of all the
       contributions that Date::Manip has made, I consider this to be the most
       important.

LIST OF Y/M/W/D FREQUENCY DEFINITIONS
       Because the week and day values may have multiple meanings depending on
       where the asterisk is, and which of the fields have non-zero values, a
       list of every possible combination is included here (though most can be
       determined using the rules above).

       When the asterisk occurs before the day element, and the day element is
       non-zero, the day element can take on multiple meanings depending on
       where the asterisk occurs, and which leading elements (year, month,
       week) have non-zero values. It can refer to the day of the week, day of
       the month, or day of the year.

       When the asterisk occurs before the week element, the week element of
       the frequency can also take on multiple meanings as well. When the
       month field and day fields are zero, it refers to the week of the year.
       Since the week of the year is well defined in the ISO 8601 spec, there
       is no ambiguity.

       When the month field is zero, but the day field is not, the week field
       refers to the nth occurrence of the day of week referred to by the day
       field in the year.

       When the month field is non-zero, the week field refers to the nth
       occurrence of the day of week in the month.

       In the tables below only the first 4 elements of the frequency are
       shown. The actual frequency will include the hour, minute, and second
       elements in addition to the ones shown.

       When all elements left of the asterisk are 0, the interval is such that
       it occurs the maximum times possible (without changing the type of
       elements to the right of the asterisk). Another way of looking at it is
       that the last 0 element of the interval is changed to 1. So, the
       interval:

	 0:0*3:0

       is equivalent to

	 0:1*3:0

       When the year field is zero, and is right of the asterisk, it means the
       current year.

       All elements left of the asterisk
	   When all of the month, week, and day elements are left of the
	   asterisk, the simple definitions of the frequency are used:

	     frequency	   meaning

	     1:2:3:4	   every 1 year, 2 months, 3 weeks,
			   4 days

	   Any, or all of the fields can be zero.

       Non-zero day, non-zero week
	   When both the day and week elements are non-zero, the day element
	   always refers to the day of week. Values must be in the range (1 to
	   7) and no negative values are allowed.

	   The following tables shows all possible variations of the frequency
	   where this can happen (where day 4 = Thursday).

	   When the week is left of the asterisk, the interval is used to get
	   the weeks on the calendar containing a recurring date, and the day
	   is used to set the day of the week.	The following are possible:

	     frequency	   meaning

	     1:2:3*4	   every 1 year, 2 months, 3 weeks
			   on Thur

	     1:0:3*4	   every 1 year, 3 weeks on Thur

	     0:2:3*4	   every 2 months, 3 weeks on Thur

	     0:0:3*4	   every 3 weeks on Thur

	   The base date is necessary for all frequencies (except 0:0:1*D) to
	   get the starting week.

	   When the week is right of the asterisk, and a non-zero month is
	   left of the asterisk, the recurrence refers to a specific
	   occurrence of a day-of-week during a month. The following are
	   possible:

	     frequency	   meaning

	     1:2*3:4	   every 1 year, 2 months on the
			   3rd Thursday of the month

	     0:2*3:4	   every 2 months on the 3rd Thur
			   of the month

	   The base date is necessary for all of these (except 0:1*W:D) to get
	   the starting month.

	   When the week and month are both non-zero and right of the
	   asterisk, the recurrence refers to an occurrence of day-of-week
	   during the given month.  Possibilities are:

	     frequency	   meaning

	     1*2:3:4	   every 1 year in February on
			   the 3rd Thur

	     0*2:3:4	   same as 1*2:3:4

	    *1:2:3:4	   in Feb 0001 on the 3rd Thur
			   of the month

	    *0:2:3:4	   on the 3rd Thur of Feb in the
			   current year

	   The base date is necessary only for Y*M:W:D where Y>1.

	   When the week is right of the asterisk, and the month is zero, the
	   recurrence refers to an occurence of the day-of-week during the
	   year. The following are possible:

	     frequency	   meaning

	     1:0*3:4	   every 1 year on the 3rd Thursday
	     1*0:3:4	   of the year

	    *1:0:3:4	   in 0001 on the 3rd Thur of
			   the year

	     0*0:3:4	   same as 1*0:3:4

	    *0:0:3:4	   on the 3rd Thur of the current
			   year

	   The base date is only required for Y*0:W:D when Y>1 to get the
	   starting year.

	   There is one special case:

	     frequency	   meaning

	     0:0*3:4	   same as 0:1*3:4 (every month on
			   the 3rd Thur of the month)

       Non-zero day, non-zero month
	   When a non-zero day element occurs to the right of the asterisk and
	   the week element is zero, but the month element is non-zero, the
	   day elements always refers to a the day of month in the range (1 to
	   31) or (-1 to -31).

	   The following table shows all possible variations of the frequency
	   where this can happen:

	     frequency	   meaning

	     1:2:0*4	   every 1 year, 2 months on the
	     1:2*0:4	   4th day of the month

	     1*2:0:4	   every year on Feb 4th

	    *1:2:0:4	   Feb 4th, 0001

	     0:2:0*4	   every 2 months on the 4th day
	     0:2*0:4	   of the month

	     0*2:0:4	   same as 1*2:0:4

	    *0:2:0:4	   Feb 4th of the current year

	   The base date is required for all except 0:1*0:D, 1*M:0:D, and
	   *Y:M:0:D and is used to get the year and month.

       Zero day, non-zero week
	   When a day is zero, and the week is non-zero, the recurrence refers
	   to a specific occurrence of the first day of the week (as given by
	   the FirstDay variable).

	   The frequency can refer to an occurrence of FirstDay in a specific
	   week (if the week is left of the asterisk):

	     frequency	   meaning

	     1:2:3*0	   every 1 year, 2 months, 3 weeks on
			   FirstDay

	     1:0:3*0	   every 1 year, 3 weeks on FirstDay

	     0:2:3*0	   every 2 months, 3 weeks on FirstDay

	     0:0:3*0	   every 3 weeks on FirstDay

	   or to a week in the year (if the week is right of the asterisk, and
	   the month is zero):

	     frequency	   meaning

	     1:0*3:0	   every 1 year on the first day of the
	     1*0:3:0	   3rd week of the year

	    *1:0:3:0	   the first day of the 3rd week of 0001

	   or to an occurrence of FirstDay in a month (if the week is right of
	   the asterisk and month is non-zero):

	     frequency	   meaning

	     1:2*3:0	   every 1 year, 2 months on the 3rd
			   occurence of FirstDay

	     0:2*3:0	   every 2 months on the 3rd occurence
			   of FirstDay

	     1*2:3:0	   every year on the 3rd occurence
			   of FirstDay in Feb

	     0*2:3:0	   same as 1*2:3:0

	    *1:2:3:0	   the 3rd occurence of FirstDay
			   Feb 0001

	    *0:2:3:0	   the 3rd occurence of FirstDay
			   in Feb of the current year

	   NOTE: in the last group, a slightly more intuitive definition of
	   these would have been to say that the week field refers to the week
	   of the month, but given the ISO 8601 manner of defining when weeks
	   start, this definition would have virtually no practical
	   application. So the definition of the week field referring to the
	   Nth occurence of FirstDay in a month was used instead.

	   There are a few special cases here:

	     frequency	   meaning

	     0:0*3:0	   same as 0:1*3:0   (every month on the 3rd
			   occurence of the first day of week)

	     0*0:3:0	   same as 1*0:3:0

	    *0:0:3:0	   the first day of the 3rd week of the
			   current year

       Non-zero day
	   When a non-zero day element occurs and both the month and week
	   elements are zero, the day elements always refers to a the day of
	   year (1 to 366 or -1 to -366 to count from the end).

	   The following table shows all possible variations of the frequency
	   where this can happen:

	     frequency	   meaning

	     1:0:0*4	   every year on the 4th day of
	     1:0*0:4	   the year
	     1*0:0:4

	    *1:0:0:4	   the 4th day of 0001

	   Other non-zero day variations have multiple meanings for the day
	   element:

	     frequency	   meaning

	     0:0:0*4	   same as 0:0:1*4  (every week on Thur)

	     0:0*0:4	   same as 0:1*0:4  (every month on the 4th)

	     0*0:0:4	   same as 1*0:0:4

	    *0:0:0:4	   the 4th day of the current year

       All other variations
	   The remaining variations have zero values for both week and day.
	   They are:

	     frequency	   meaning

	     1:2:0*0	   every 1 year, 2 months on the first
	     1:2*0:0	   day of the month

	     1*2:0:0	   every year on Feb 1

	    *1:2:0:0	   Feb 1, 0001

	     1:0:0*0	   every 1 year on Jan 1
	     1:0*0:0
	     1*0:0:0

	    *1:0:0:0	   Jan 1, 0001

	     0:2:0*0	   every 2 months on the first day of
	     0:2*0:0	   the month

	     0*2:0:0	   same as 1*2:0:0

	    *0:2:0:0	   Feb 1 of the current year

	     0:0:0*0	   same as 0:0:1*0 (every week on
			   the first day of the week)

	     0:0*0:0	   same as 0:1*0:0 (every month
			   on the 1st)

	     0*0:0:0	   same as 1*0:0:0

	    *0:0:0:0	   Jan 1 of the current year

METHODS
       new
       new_config
       new_date
       new_delta
       new_recur
       base
       tz
       is_date
       is_delta
       is_recur
       config
       err Please refer to the Date::Manip::Obj documentation for these
	   methods.

       parse
	      $err = $recur->parse($string [,$modifiers] [,$base,$start,$end]);

	   This creates a new recurrence. A string containing a valid
	   frequency is required. In addition, $start, $end, and $base dates
	   can be passed in (either as Date::Manip::Date objects, or as
	   strings containing dates that can be parsed), and any number of the
	   modifiers listed above.

	   If the $start or $end dates are not included, they may be supplied
	   automatically, based on the value of the RecurRange variable. If
	   any of the dates are passed in, they must be included in the order
	   given (though it is safe to pass an empty string or undef in for
	   any of them if you only want to set some, but not all of them).

	   The $modifiers argument must either contain valid modifiers, or be
	   left out of the argument list entirely. You cannot pass an empty
	   string or undef in for it.

	      $err = $recur->parse($string);

	   This creates a recurrence from a string which contains all of the
	   necessary elements of the recurrence. The string is of the format:

	      FREQ*MODIFIERS*BASE*START*END

	   where FREQ is a string containing a frequency, MODIFIERS is a
	   string containing a comma separated list of modifiers, BASE, START,
	   and END are strings containing parseable dates.

	   All pieces are optional, but order must be maintained, so all of
	   the following are valid:

	      FREQ*MODIFIERS
	      FREQ**BASE
	      FREQ**BASE*START*END

       frequency
       start
       end
       base
       modifiers
	   You can also create a recurrency in steps (or replace parts of an
	   existing recurrence) using the following:

	      $err = $recur->frequency($frequency);

	      $err = $recur->start($start);
	      $err = $recur->end($end);

	      $err = $recur->base($base);

	      $err = $recur->modifiers($modifiers);
	      $err = $recur->modifiers(@modifiers);

	   These set the appropriate part of the recurrence.

	   Calling the frequency method discards all information currently
	   stored in the Recur object (including an existing start, end, and
	   base date), so this method should be called first.

	   In the modifiers method, the modifiers can be passed in as a string
	   containing a comma separated list of modifiers, or as a list of
	   modifiers. The modifiers passed in override all previously set
	   modifiers UNLESS the first one is the string "+", in which case the
	   new modifiers are appended to the list.

	   In the start, end, and base methods, the date passed in can be a
	   Date::Manip::Date object, or a string that can be parsed to get a
	   date.

       dates
	      @dates = $recur->dates([$start,$end]);

	   Returns the list of dates defined by the full recurrence. If there
	   is an error, @dates will be empty, and the error flag will be set
	   in the $recur object.

	   $start and $end are either undef, or dates which can be used to
	   limit the set of dates passed back.

	   If the recurrence does not have a start and end date already,
	   passing in $start and $end will set the range (but they will NOT be
	   stored in the recurrence).

	   If the recurrence does have a start and end date stored in it, the
	   $start and $end arguments can be used to further limit the dates
	   returned. In other words, if a recurrence has a start date of Jan
	   1, 2006 00:00:00 and and end date of Dec 31, 2006 23:59:59 stored
	   in the recurrence, passing in $start of Jul 1, 2006 00:00:00 will
	   limit the dates returned to the range of Jul 1 to Dec 31.

	   Passing in a start date of Jul 1, 2007 will mean that no dates are
	   returned since the recurrence limits the date to be in 2006.

KNOWN BUGS
       None known.

BUGS AND QUESTIONS
       Please refer to the Date::Manip::Problems documentation for information
       on submitting bug reports or questions to the author.

SEE ALSO
       Date::Manip	  - main module documentation

LICENSE
       This script is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

AUTHOR
       Sullivan Beck (sbeck@cpan.org)

perl v5.10.1			  2010-01-12		 Date::Manip::Recur(3)
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