Calc(3) User Contributed Perl Documentation Calc(3)
NAME
Date::Calc - Gregorian calendar date calculations
MOTTO
Keep it small, fast and simple
PREFACE
This package consists of a C library and a Perl module (which uses the
C library, internally) for all kinds of date calculations based on the
Gregorian calendar (the one used in all western countries today),
thereby complying with all relevant norms and standards:
ISO/R 2015-1971, DIN 1355 and, to some extent, ISO 8601 (where
applicable).
(See also http://www.engelschall.com/u/sb/download/Date-Calc/DIN1355/
for a scan of part of the "DIN 1355" document (in German)).
The module of course handles year numbers of 2000 and above correctly
("Year 2000" or "Y2K" compliance) -- actually all year numbers from 1
to the largest positive integer representable on your system (which is
at least 32767) can be dealt with.
This is not true, however, for the import/export functions in this
package which are an interface to the internal POSIX date and time
functions of your system, which can only cover dates in the following
ranges:
01-Jan-1970 00:00:00 GMT .. 19-Jan-2038 03:14:07 GMT [Unix etc.]
01-Jan-1904 00:00:00 LT .. 06-Feb-2040 06:28:15 LT [MacOS Classic]
(LT = local time)
Note that this package projects the Gregorian calendar back until the
year 1 A.D. -- even though the Gregorian calendar was only adopted in
1582, mostly by the Catholic European countries, in obedience to the
corresponding decree of Pope Gregory XIII in that year.
Some (mainly protestant) countries continued to use the Julian calendar
(used until then) until as late as the beginning of the 20th century.
Finally, note that this package is not intended to do everything you
could ever imagine automagically for you; it is rather intended to
serve as a toolbox (in the best of UNIX spirit and traditions) which
should, however, always get you where you want to go.
See the section "RECIPES" at the bottom of this document for solutions
to common problems!
If nevertheless you can't figure out how to solve a particular problem,
please let me know! (See e-mail address at the end of this document.)
SYNOPSIS
use Date::Calc qw(
Days_in_Year
Days_in_Month
Weeks_in_Year
leap_year
check_date
check_time
check_business_date
Day_of_Year
Date_to_Days
Day_of_Week
Week_Number
Week_of_Year
Monday_of_Week
Nth_Weekday_of_Month_Year
Standard_to_Business
Business_to_Standard
Delta_Days
Delta_DHMS
Delta_YMD
Delta_YMDHMS
Normalize_DHMS
Add_Delta_Days
Add_Delta_DHMS
Add_Delta_YM
Add_Delta_YMD
Add_Delta_YMDHMS
System_Clock
Today
Now
Today_and_Now
This_Year
Gmtime
Localtime
Mktime
Timezone
Date_to_Time
Time_to_Date
Easter_Sunday
Decode_Month
Decode_Day_of_Week
Decode_Language
Decode_Date_EU
Decode_Date_US
Fixed_Window
Moving_Window
Compress
Uncompress
check_compressed
Compressed_to_Text
Date_to_Text
Date_to_Text_Long
English_Ordinal
Calendar
Month_to_Text
Day_of_Week_to_Text
Day_of_Week_Abbreviation
Language_to_Text
Language
Languages
Decode_Date_EU2
Decode_Date_US2
Parse_Date
ISO_LC
ISO_UC
);
use Date::Calc qw(:all);
Days_in_Year
$days = Days_in_Year($year,$month);
Days_in_Month
$days = Days_in_Month($year,$month);
Weeks_in_Year
$weeks = Weeks_in_Year($year);
leap_year
if (leap_year($year))
check_date
if (check_date($year,$month,$day))
check_time
if (check_time($hour,$min,$sec))
check_business_date
if (check_business_date($year,$week,$dow))
Day_of_Year
$doy = Day_of_Year($year,$month,$day);
Date_to_Days
$days = Date_to_Days($year,$month,$day);
Day_of_Week
$dow = Day_of_Week($year,$month,$day);
Week_Number
$week = Week_Number($year,$month,$day); # DEPRECATED
Week_of_Year
($week,$year) = Week_of_Year($year,$month,$day); # RECOMMENDED
$week = Week_of_Year($year,$month,$day); # DANGEROUS
Monday_of_Week
($year,$month,$day) = Monday_of_Week($week,$year);
Nth_Weekday_of_Month_Year
if (($year,$month,$day) =
Nth_Weekday_of_Month_Year($year,$month,$dow,$n))
Standard_to_Business
($year,$week,$dow) =
Standard_to_Business($year,$month,$day);
Business_to_Standard
($year,$month,$day) =
Business_to_Standard($year,$week,$dow);
Delta_Days
$Dd = Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2);
Delta_DHMS
($Dd,$Dh,$Dm,$Ds) =
Delta_DHMS($year1,$month1,$day1, $hour1,$min1,$sec1,
$year2,$month2,$day2, $hour2,$min2,$sec2);
Delta_YMD
($Dy,$Dm,$Dd) =
Delta_YMD($year1,$month1,$day1,
$year2,$month2,$day2);
Delta_YMDHMS
($D_y,$D_m,$D_d, $Dh,$Dm,$Ds) =
Delta_YMDHMS($year1,$month1,$day1, $hour1,$min1,$sec1,
$year2,$month2,$day2, $hour2,$min2,$sec2);
Normalize_DHMS
($Dd,$Dh,$Dm,$Ds) =
Normalize_DHMS($Dd,$Dh,$Dm,$Ds);
Add_Delta_Days
($year,$month,$day) =
Add_Delta_Days($year,$month,$day,
$Dd);
Add_Delta_DHMS
($year,$month,$day, $hour,$min,$sec) =
Add_Delta_DHMS($year,$month,$day, $hour,$min,$sec,
$Dd,$Dh,$Dm,$Ds);
Add_Delta_YM
($year,$month,$day) =
Add_Delta_YM($year,$month,$day,
$Dy,$Dm);
Add_Delta_YMD
($year,$month,$day) =
Add_Delta_YMD($year,$month,$day,
$Dy,$Dm,$Dd);
Add_Delta_YMDHMS
($year,$month,$day, $hour,$min,$sec) =
Add_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec,
$D_y,$D_m,$D_d, $Dh,$Dm,$Ds);
System_Clock
($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
System_Clock([$gmt]);
Today
($year,$month,$day) = Today([$gmt]);
Now
($hour,$min,$sec) = Now([$gmt]);
Today_and_Now
($year,$month,$day, $hour,$min,$sec) = Today_and_Now([$gmt]);
This_Year
$year = This_Year([$gmt]);
Gmtime
($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
Gmtime([time]);
Localtime
($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
Localtime([time]);
Mktime
$time = Mktime($year,$month,$day, $hour,$min,$sec);
Timezone
($D_y,$D_m,$D_d, $Dh,$Dm,$Ds, $dst) = Timezone([time]);
Date_to_Time
$time = Date_to_Time($year,$month,$day, $hour,$min,$sec);
Time_to_Date
($year,$month,$day, $hour,$min,$sec) = Time_to_Date([time]);
Easter_Sunday
($year,$month,$day) = Easter_Sunday($year);
Decode_Month
if ($month = Decode_Month($string))
Decode_Day_of_Week
if ($dow = Decode_Day_of_Week($string))
Decode_Language
if ($lang = Decode_Language($string))
Decode_Date_EU
if (($year,$month,$day) = Decode_Date_EU($string))
Decode_Date_US
if (($year,$month,$day) = Decode_Date_US($string))
Fixed_Window
$year = Fixed_Window($yy);
Moving_Window
$year = Moving_Window($yy);
Compress
$date = Compress($year,$month,$day);
Uncompress
if (($century,$year,$month,$day) = Uncompress($date))
check_compressed
if (check_compressed($date))
Compressed_to_Text
$string = Compressed_to_Text($date);
Date_to_Text
$string = Date_to_Text($year,$month,$day);
Date_to_Text_Long
$string = Date_to_Text_Long($year,$month,$day);
English_Ordinal
$string = English_Ordinal($number);
Calendar
$string = Calendar($year,$month[,$orthodox]);
Month_to_Text
$string = Month_to_Text($month);
Day_of_Week_to_Text
$string = Day_of_Week_to_Text($dow);
Day_of_Week_Abbreviation
$string = Day_of_Week_Abbreviation($dow);
Language_to_Text
$string = Language_to_Text($lang);
Language
$lang = Language();
Language($lang);
$oldlang = Language($newlang);
Languages
$max_lang = Languages();
Decode_Date_EU2
if (($year,$month,$day) = Decode_Date_EU2($string))
Decode_Date_US2
if (($year,$month,$day) = Decode_Date_US2($string))
Parse_Date
if (($year,$month,$day) = Parse_Date($string))
ISO_LC
$lower = ISO_LC($string);
ISO_UC
$upper = ISO_UC($string);
Version
$string = Date::Calc::Version();
IMPORTANT NOTES
(See the section "RECIPES" at the bottom of this document for solutions
to common problems!)
o "Year 2000" ("Y2K") compliance
The upper limit for any year number in this module is only given by
the size of the largest positive integer that can be represented in a
variable of the C type "int" on your system, which is at least 32767,
according to the ANSI C standard (exceptions see below).
In order to simplify calculations, this module projects the gregorian
calendar back until the year 1 A.D. -- i.e., back BEYOND the year
1582 when this calendar was first decreed by the Catholic Pope
Gregory XIII!
Therefore, BE SURE TO ALWAYS SPECIFY "1998" WHEN YOU MEAN "1998", for
instance, and DO NOT WRITE "98" INSTEAD, because this will in fact
perform a calculation based on the year "98" A.D. and NOT "1998"!
An exception from this rule are the functions which contain the word
"compress" in their names (which can only handle years between 1970
and 2069 and also accept the abbreviations "00" to "99"), and the
functions whose names begin with "Decode_Date_" (which translate year
numbers below 100 using a technique known as "moving window").
If you want to convert a two-digit year number into a full-fledged,
four-digit (at least for some years to come ";-)") year number, use
the two functions "Fixed_Window()" and "Moving_Window()" (see their
description further below).
Note also that the following import/export functions (which are
interfaces to the POSIX functions "time()", "gmtime()", "localtime()"
and "mktime()" or (the last two) substitutes for the BSD function
"timegm()" and the POSIX function "gmtime()") have a very limited
range of representable dates (in contrast to all other functions in
this package, which cover virtually any date including and after
January 1st 1 A.D.):
System_Clock()
Today()
Now()
Today_and_Now()
This_Year()
Gmtime()
Localtime()
Mktime()
Timezone()
Date_to_Time()
Time_to_Date()
These functions can only deal with dates in the range from
01-Jan-1970 00:00:00 GMT to 19-Jan-2038 03:14:07 GMT (the latter
limit is only authoritative on 32 bit systems, however, and can (in
principle, through a few code changes) be extended somewhat ":-)" on
64 bit systems).
On MacOS Classic, the valid range of dates is between (both included)
01-Jan-1904 00:00:00 (local time) to 06-Feb-2040 06:28:15 (local
time).
Note further that the function "Easter_Sunday()" can only be used for
years in the range 1583 to 2299.
o First index
ALL ranges in this module start with "1", NOT "0"!
I.e., the day of month, day of week, day of year, month of year, week
of year, first valid year number and language ALL start counting at
one, NOT zero!
The only exception is the function ""Week_Number()"", which may in
fact return "0" when the given date actually lies in the last week of
the PREVIOUS year, and of course the numbers for hours (0..23),
minutes (0..59) and seconds (0..59).
o Function naming conventions
Function names completely in lower case indicate a boolean return
value.
o Boolean values
Boolean values in this module are always a numeric zero ("0") for
"false" and a numeric one ("1") for "true".
o Exception handling
The functions in this module will usually die with a corresponding
error message if their input parameters, intermediate results or
output values are out of range.
The following functions handle errors differently:
- check_date()
- check_time()
- check_business_date()
- check_compressed()
(which return a "false" return value when the given input does not
represent a valid date or time),
- Nth_Weekday_of_Month_Year()
(which returns an empty list if the requested 5th day of week does
not exist),
- Decode_Month()
- Decode_Day_of_Week()
- Decode_Language()
- Fixed_Window()
- Moving_Window()
- Compress()
(which return "0" upon failure or invalid input), and
- Decode_Date_EU()
- Decode_Date_US()
- Decode_Date_EU2()
- Decode_Date_US2()
- Parse_Date()
- Uncompress()
(which return an empty list upon failure or invalid input).
Note that you can always catch an exception thrown by any of the
functions in this module and handle it yourself by enclosing the
function call in an ""eval"" with curly brackets and checking the
special variable "$@" (see "eval" in perlfunc(1) for details).
DESCRIPTION
o "use Date::Calc qw( Days_in_Year Days_in_Month ... );"
o "use Date::Calc qw(:all);"
You can either specify the functions you want to import explicitly by
enumerating them between the parentheses of the ""qw()"" operator, or
you can use the "":all"" tag instead to import ALL available
functions.
o "$days = Days_in_Year($year,$month);"
This function returns the sum of the number of days in the months
starting with January up to and including "$month" in the given year
"$year".
I.e., ""Days_in_Year(1998,1)"" returns "31", ""Days_in_Year(1998,2)""
returns "59", ""Days_in_Year(1998,3)"" returns "90", and so on.
Note that ""Days_in_Year($year,12)"" returns the number of days in
the given year "$year", i.e., either "365" or "366".
o "$days = Days_in_Month($year,$month);"
This function returns the number of days in the given month "$month"
of the given year "$year".
The year must always be supplied, even though it is only needed when
the month is February, in order to determine whether it is a leap
year or not.
I.e., ""Days_in_Month(1998,1)"" returns "31",
""Days_in_Month(1998,2)"" returns "28", ""Days_in_Month(2000,2)""
returns "29", ""Days_in_Month(1998,3)"" returns "31", and so on.
o "$weeks = Weeks_in_Year($year);"
This function returns the number of weeks in the given year "$year",
i.e., either "52" or "53".
o "if (leap_year($year))"
This function returns "true" ("1") if the given year "$year" is a
leap year and "false" ("0") otherwise.
o "if (check_date($year,$month,$day))"
This function returns "true" ("1") if the given three numerical
values "$year", "$month" and "$day" constitute a valid date, and
"false" ("0") otherwise.
o "if (check_time($hour,$min,$sec))"
This function returns "true" ("1") if the given three numerical
values "$hour", "$min" and "$sec" constitute a valid time ("0 <=
$hour < 24", "0 <= $min < 60" and "0 <= $sec < 60"), and "false"
("0") otherwise.
o "if (check_business_date($year,$week,$dow))"
This function returns "true" ("1") if the given three numerical
values "$year", "$week" and "$dow" constitute a valid date in
business format, and "false" ("0") otherwise.
Beware that this function does NOT compute whether a given date is a
business day (i.e., Monday to Friday)!
To do so, use ""(Day_of_Week($year,$month,$day) < 6)"" instead.
o "$doy = Day_of_Year($year,$month,$day);"
This function returns the (relative) number of the day of the given
date in the given year.
E.g., ""Day_of_Year($year,1,1)"" returns "1",
""Day_of_Year($year,2,1)"" returns "32", and
""Day_of_Year($year,12,31)"" returns either "365" or "366".
The day of year is sometimes also referred to as the Julian day (or
date), although it has nothing to do with the Julian calendar, the
calendar which was used before the Gregorian calendar.
In order to convert the number returned by this function back into a
date, use the function ""Add_Delta_Days()"" (described further
below), as follows:
$doy = Day_of_Year($year,$month,$day);
($year,$month,$day) = Add_Delta_Days($year,1,1, $doy - 1);
o "$days = Date_to_Days($year,$month,$day);"
This function returns the (absolute) number of the day of the given
date, where counting starts at the 1st of January of the year 1 A.D.
I.e., ""Date_to_Days(1,1,1)"" returns "1", ""Date_to_Days(1,12,31)""
returns "365", ""Date_to_Days(2,1,1)"" returns "366",
""Date_to_Days(1998,5,1)"" returns "729510", and so on.
This is sometimes also referred to (not quite correctly) as the
Julian date (or day). This may cause confusion, because also the
number of the day in a year (from 1 to 365 or 366) is frequently
called the "Julian day".
More confusing still, this has nothing to do with the Julian
calendar, which was used BEFORE the Gregorian calendar.
The Julian calendar was named after famous Julius Caesar, who had
instituted it in Roman times. The Julian calendar is less precise
than the Gregorian calendar because it has too many leap years
compared to the true mean length of a year (but the Gregorian
calendar also still has one day too much every 5000 years). Anyway,
the Julian calendar was better than what existed before, because
rulers had often changed the calendar used until then in arbitrary
ways, in order to lengthen their own reign, for instance.
In order to convert the number returned by this function back into a
date, use the function ""Add_Delta_Days()"" (described further
below), as follows:
$days = Date_to_Days($year,$month,$day);
($year,$month,$day) = Add_Delta_Days(1,1,1, $days - 1);
o "$dow = Day_of_Week($year,$month,$day);"
This function returns the number of the day of week of the given
date.
The function returns "1" for Monday, "2" for Tuesday and so on until
"7" for Sunday.
Note that in the Hebrew calendar (on which the Christian calendar is
based), the week starts with Sunday and ends with the Sabbath or
Saturday (where according to the Genesis (as described in the Bible)
the Lord rested from creating the world).
In medieval times, Catholic Popes have decreed the Sunday to be the
official day of rest, in order to dissociate the Christian from the
Hebrew belief.
Nowadays, the Sunday AND the Saturday are commonly considered (and
used as) days of rest, usually referred to as the "week-end".
Consistent with this practice, current norms and standards (such as
ISO/R 2015-1971, DIN 1355 and ISO 8601) define the Monday as the
first day of the week.
o "$week = Week_Number($year,$month,$day);"
This function returns the number of the week the given date lies in.
If the given date lies in the LAST week of the PREVIOUS year, "0" is
returned.
If the given date lies in the FIRST week of the NEXT year,
""Weeks_in_Year($year) + 1"" is returned.
o "($week,$year) = Week_of_Year($year,$month,$day);"
This function returns the number of the week the given date lies in,
as well as the year that week belongs to.
I.e., if the given date lies in the LAST week of the PREVIOUS year,
""(Weeks_in_Year($year-1), $year-1)"" is returned.
If the given date lies in the FIRST week of the NEXT year, ""(1,
$year+1)"" is returned.
Otherwise, ""(Week_Number($year,$month,$day), $year)"" is returned.
o "$week = Week_of_Year($year,$month,$day);"
In scalar context, this function returns just the week number. This
allows you to write ""$week = Week_of_Year($year,$month,$day);""
instead of ""($week) = Week_of_Year($year,$month,$day);"" (note the
parentheses around "$week").
If the given date lies in the LAST week of the PREVIOUS year,
""Weeks_in_Year($year-1)"" is returned.
If the given date lies in the FIRST week of the NEXT year, "1" is
returned.
Otherwise the return value is identical with that of
""Week_Number($year,$month,$day)"".
BEWARE that using this function in scalar context is a DANGEROUS
feature, because without knowing which year the week belongs to, you
might inadvertently assume the wrong one!
If for instance you are iterating through an interval of dates, you
might assume that the week always belongs to the same year as the
given date, which unfortunately is WRONG in some cases!
In many years, the 31st of December for instance belongs to week
number one of the FOLLOWING year. Assuming that the year is the same
as your date (31st of December, in this example), sends you back to
the first week of the CURRENT year - the Monday of which, by the way,
in case of bad luck, might actually lie in the year BEFORE the
current year!
This actually happens in 2002, for example.
So you always need to provide the correct corresponding year number
by other means, keeping track of it yourself.
In case you do not understand this, never mind, but then simply DO
NOT USE this function in scalar context!
o "($year,$month,$day) = Monday_of_Week($week,$year);"
This function returns the date of the first day of the given week,
i.e., the Monday.
"$year" must be greater than or equal to "1", and "$week" must lie in
the range "1" to ""Weeks_in_Year($year)"".
Note that you can write ""($year,$month,$day) =
Monday_of_Week(Week_of_Year($year,$month,$day));"" in order to
calculate the date of the Monday of the same week as the given date.
If you want to calculate any other day of week in the same week as a
given date, use
@date = Add_Delta_Days(Monday_of_Week(Week_of_Year(@date)),$offset);
where "$offset = 1" for Tuesday, 2 for Wednesday etc.
o "if (($year,$month,$day) =
Nth_Weekday_of_Month_Year($year,$month,$dow,$n))"
This function calculates the date of the "$n"th day of week "$dow" in
the given month "$month" and year "$year"; such as, for example, the
3rd Thursday of a given month and year.
This can be used to send a notification mail to the members of a
group which meets regularly on every 3rd Thursday of a month, for
instance.
(See the section "RECIPES" near the end of this document for a code
snippet to actually do so.)
"$year" must be greater than or equal to "1", "$month" must lie in
the range "1" to "12", "$dow" must lie in the range "1" to "7" and
"$n" must lie in the range "1" to "5", or a fatal error (with
appropriate error message) occurs.
The function returns an empty list when the 5th of a given day of
week does not exist in the given month and year.
o "($year,$week,$dow) = Standard_to_Business($year,$month,$day);"
This function converts a given date from standard notation (year,
month, day (of month)) to business notation (year, week, day of
week).
o "($year,$month,$day) = Business_to_Standard($year,$week,$dow);"
This function converts a given date from business notation (year,
week, day of week) to standard notation (year, month, day (of
month)).
o "$Dd = Delta_Days($year1,$month1,$day1, $year2,$month2,$day2);"
This function returns the difference in days between the two given
dates.
The result is positive if the two dates are in chronological order,
i.e., if date #1 comes chronologically BEFORE date #2, and negative
if the order of the two dates is reversed.
The result is zero if the two dates are identical.
o "($Dd,$Dh,$Dm,$Ds) = Delta_DHMS($year1,$month1,$day1,
$hour1,$min1,$sec1, $year2,$month2,$day2, $hour2,$min2,$sec2);"
This function returns the difference in days, hours, minutes and
seconds between the two given dates with times.
All four return values will be positive if the two dates are in
chronological order, i.e., if date #1 comes chronologically BEFORE
date #2, and negative (in all four return values!) if the order of
the two dates is reversed.
This is so that the two functions ""Delta_DHMS()"" and
""Add_Delta_DHMS()"" (description see further below) are
complementary, i.e., mutually inverse:
Add_Delta_DHMS(@date1,@time1, Delta_DHMS(@date1,@time1, @date2,@time2))
yields ""(@date2,@time2)"" again, whereas
Add_Delta_DHMS(@date2,@time2,
map(-$_, Delta_DHMS(@date1,@time1, @date2,@time2)))
yields ""(@date1,@time1)"", and
Delta_DHMS(@date1,@time1, Add_Delta_DHMS(@date1,@time1, @delta))
yields "@delta" again.
The result is zero (in all four return values) if the two dates and
times are identical.
o "($Dy,$Dm,$Dd) = Delta_YMD($year1,$month1,$day1,
$year2,$month2,$day2);"
This function returns the vector
( $year2 - $year1, $month2 - $month1, $day2 - $day1 )
An error occurs if any of the two dates is invalid.
o "($D_y,$D_m,$D_d, $Dh,$Dm,$Ds) = Delta_YMDHMS($year1,$month1,$day1,
$hour1,$min1,$sec1, $year2,$month2,$day2, $hour2,$min2,$sec2);"
This function is based on the function "Delta_YMD()" above but
additionally calculates the time difference. When a carry over from
the time difference occurs, the value of "$D_d" is adjusted
accordingly, thus giving the correct total date/time difference.
Arguments are expected to be in chronological order to yield a
(usually) positive result.
In any case, adding the result of this function to the first
date/time value ("$year1,$month1,$day1," "$hour1,$min1,$sec1") always
gives the second date/time value ("$year2,$month2,$day2,"
"$hour2,$min2,$sec2") again, and adding the negative result (all
elements of the result vector negated) to the second date/time value
gives the first date/time value.
See the function "Add_Delta_YMDHMS()" further below for adding a
date/time value and a date/time difference.
An error occurs if any of the two date/time values is invalid.
o "($Dd,$Dh,$Dm,$Ds) = Normalize_DHMS($Dd,$Dh,$Dm,$Ds);"
This function takes four arbitrary values for days, hours, minutes
and seconds (which may have different signs) and renormalizes them so
that the values for hours, minutes and seconds will lie in the ranges
"[-23..23]", "[-59..59]" and "[-59..59]", respectively, and so that
all four values have the same sign (or are zero).
The given values are left untouched, i.e., unchanged.
o "($year,$month,$day) = Add_Delta_Days($year,$month,$day, $Dd);"
This function has two principal uses:
First, it can be used to calculate a new date, given an initial date
and an offset (which may be positive or negative) in days, in order
to answer questions like "today plus 90 days -- which date gives
that?".
(In order to add a weeks offset, simply multiply the weeks offset
with "7" and use that as your days offset.)
Second, it can be used to convert the canonical representation of a
date, i.e., the number of that day (where counting starts at the 1st
of January in 1 A.D.), back into a date given as year, month and day.
Because counting starts at "1", you will actually have to subtract
"1" from the canonical date in order to get back the original date:
$canonical = Date_to_Days($year,$month,$day);
($year,$month,$day) = Add_Delta_Days(1,1,1, $canonical - 1);
Moreover, this function is the inverse of the function
""Delta_Days()"":
Add_Delta_Days(@date1, Delta_Days(@date1, @date2))
yields "@date2" again, whereas
Add_Delta_Days(@date2, -Delta_Days(@date1, @date2))
yields "@date1", and
Delta_Days(@date1, Add_Delta_Days(@date1, $delta))
yields "$delta" again.
o "($year,$month,$day, $hour,$min,$sec) =
Add_Delta_DHMS($year,$month,$day, $hour,$min,$sec, $Dd,$Dh,$Dm,$Ds);"
This function serves to add a days, hours, minutes and seconds offset
to a given date and time, in order to answer questions like "today
and now plus 7 days but minus 5 hours and then plus 30 minutes, what
date and time gives that?":
($y,$m,$d,$H,$M,$S) = Add_Delta_DHMS(Today_and_Now(), +7,-5,+30,0);
o "($year,$month,$day) = Add_Delta_YM($year,$month,$day, $Dy,$Dm);"
This function can be used to add a year and/or month offset to a
given date.
In contrast to the function described immediately below
(""Add_Delta_YMD()""), this function does no "wrapping" into the next
month if the day happens to lie outside the valid range for the
resulting year and month (after adding the year and month offsets).
Instead, it simply truncates the day to the last possible day of the
resulting month.
Examples:
Adding an offset of 0 years, 1 month to the date (1999,1,31) would
result in the (invalid) date (1999,2,31). The function replaces this
result by the (valid) date (1999,2,28).
Adding an offset of 1 year, 1 month to the same date (1999,1,31) as
above would result in the (still invalid) date (2000,2,31). The
function replaces this result by the valid date (2000,2,29) (because
2000 is a leap year).
Note that the year and month offsets can be negative, and that they
can have different signs.
If you want to additionally add a days offset, use the function
""Add_Delta_Days()"" before or after calling ""Add_Delta_YM()"":
@date2 = Add_Delta_Days( Add_Delta_YM(@date1, $Dy,$Dm), $Dd );
@date2 = Add_Delta_YM( Add_Delta_Days(@date1, $Dd), $Dy,$Dm );
Note that your result may depend on the order in which you call these
two functions!
Consider the date (1999,2,28) and the offsets 0 years, 1 month and 1
day:
(1999,2,28) plus one month is (1999,3,28), plus one day is
(1999,3,29). (1999,2,28) plus one day is (1999,3,1), plus one month
is (1999,4,1).
(Which is also the reason why the ""Add_Delta_YM()"" function does
not allow to add a days offset, because this would actually require
TWO functions: One for adding the days offset BEFORE and one for
adding it AFTER applying the year/month offsets.)
An error occurs if the initial date is not valid.
Note that ""Add_Delta_YM( Add_Delta_YM(@date, $Dy,$Dm), -$Dy,-$Dm
);"" will not, in general, return the original date "@date" (consider
the examples given above!).
o "($year,$month,$day) = Add_Delta_YMD($year,$month,$day,
$Dy,$Dm,$Dd);"
This function serves to add a years, months and days offset to a
given date.
(In order to add a weeks offset, simply multiply the weeks offset
with "7" and add this number to your days offset.)
Note that the three offsets for years, months and days are applied
independently from each other. This also allows them to have
different signs.
The years and months offsets are applied first, and the days offset
is applied last.
If the resulting date happens to fall on a day after the end of the
resulting month, like the 32nd of April or the 30th of February, then
the date is simply counted forward into the next month (possibly also
into the next year) by the number of excessive days (e.g., the 32nd
of April will become the 2nd of May).
BEWARE that this behaviour differs from that of previous versions of
this module! In previous versions, the day was simply truncated to
the maximum number of days in the resulting month.
If you want the previous behaviour, use the new function
""Add_Delta_YM()"" (described immediately above) plus the function
""Add_Delta_Days()"" instead.
BEWARE also that because a year and a month offset is not equivalent
to a fixed number of days, the transformation performed by this
function is NOT ALWAYS REVERSIBLE!
This is in contrast to the functions ""Add_Delta_Days()"" and
""Add_Delta_DHMS()"", which are fully and truly reversible (with the
help of the functions ""Delta_Days()"" and ""Delta_DHMS()"", for
instance).
Note that for this same reason,
@date = Add_Delta_YMD(
Add_Delta_YMD(@date, $Dy,$Dm,$Dd), -$Dy,-$Dm,-$Dd);
will in general NOT return the initial date "@date".
Note that this is NOT a program bug but NECESSARILY so because of the
variable lengths of years and months!
o "($year,$month,$day, $hour,$min,$sec) =
Add_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec, $D_y,$D_m,$D_d,
$Dh,$Dm,$Ds);"
Same as the function above, except that a time offset may be given in
addition to the year, month and day offset.
o "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
System_Clock([$gmt]);"
If your operating system supports the corresponding system calls
(""time()"" and ""localtime()"" or ""gmtime()""), this function will
return the information provided by your system clock, i.e., the
current date and time, the number of the day of year, the number of
the day of week and a flag signaling whether daylight savings time is
currently in effect or not.
The ranges of values returned (and their meanings) are as follows:
$year : 1970..2038 (or more) [Unix etc.]
$year : 1904..2040 [MacOS Classic]
$month : 1..12
$day : 1..31
$hour : 0..23
$min : 0..59
$sec : 0..59 (0..61 on some systems)
$doy : 1..366
$dow : 1..7
$dst : -1..1
"$doy" is the day of year, sometimes also referred to as the "julian
date", which starts at "1" and goes up to the number of days in that
year.
The day of week ("$dow") will be "1" for Monday, "2" for Tuesday and
so on until "7" for Sunday.
The daylight savings time flag ("$dst") will be ""-1"" if this
information is not available on your system, "0" for no daylight
savings time (i.e., winter time) and "1" when daylight savings time
is in effect.
If your operating system does not provide the necessary system calls,
calling this function will result in a fatal "not available on this
system" error message.
If you want to handle this exception yourself, use ""eval"" as
follows:
eval { ($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
System_Clock(); };
if ($@)
{
# Handle missing system clock
# (For instance, ask user to enter this information manually)
}
Note that curlies ("{" and "}") are used here to delimit the
statement to be "eval"ed (which is the way to catch exceptions in
Perl), and not quotes (which is a way to evaluate Perl expressions at
runtime).
If the optional (boolean) input parameter "$gmt" is given, a "true"
value ("1") will cause ""gmtime()"" to be used instead of
""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
or UTC) instead of local time.
o "($year,$month,$day) = Today([$gmt]);"
This function returns a subset of the values returned by the function
""System_Clock()"" (see above for details), namely the current year,
month and day.
A fatal "not available on this system" error message will appear if
the corresponding system calls are not supported by your current
operating system.
If the optional (boolean) input parameter "$gmt" is given, a "true"
value ("1") will cause ""gmtime()"" to be used instead of
""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
or UTC) instead of local time.
o "($hour,$min,$sec) = Now([$gmt]);"
This function returns a subset of the values returned by the function
""System_Clock()"" (see above for details), namely the current time
(hours, minutes and full seconds).
A fatal "not available on this system" error message will appear if
the corresponding system calls are not supported by your current
operating system.
If the optional (boolean) input parameter "$gmt" is given, a "true"
value ("1") will cause ""gmtime()"" to be used instead of
""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
or UTC) instead of local time.
o "($year,$month,$day, $hour,$min,$sec) = Today_and_Now([$gmt]);"
This function returns a subset of the values returned by the function
""System_Clock()"" (see above for details), namely the current date
(year, month, day) and time (hours, minutes and full seconds).
A fatal "not available on this system" error message will appear if
the corresponding system calls are not supported by your current
operating system.
If the optional (boolean) input parameter "$gmt" is given, a "true"
value ("1") will cause ""gmtime()"" to be used instead of
""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
or UTC) instead of local time.
o "$year = This_Year([$gmt]);"
This function returns the current year, according to local time.
A fatal "not available on this system" error message will appear if
the corresponding system calls are not supported by your current
operating system.
If the optional (boolean) input parameter "$gmt" is given, a "true"
value ("1") will cause ""gmtime()"" to be used instead of
""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
or UTC) instead of local time. However, this will only make a
difference within a few hours around New Year (unless you are on a
Pacific island, where this can be almost 24 hours).
o "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
Gmtime([time]);"
This is Date::Calc's equivalent of Perl's built-in "gmtime()"
function. See also "gmtime" in perlfunc.
The ranges of values returned (and their meanings) are as follows:
$year : 1970..2038 (or more) [Unix etc.]
$year : 1904..2040 [MacOS Classic]
$month : 1..12
$day : 1..31
$hour : 0..23
$min : 0..59
$sec : 0..59
$doy : 1..366
$dow : 1..7
$dst : -1..1
"$doy" is the day of year, sometimes also referred to as the "julian
date", which starts at "1" and goes up to the number of days in that
year.
The day of week ("$dow") will be "1" for Monday, "2" for Tuesday and
so on until "7" for Sunday.
The daylight savings time flag ("$dst") will be ""-1"" if this
information is not available on your system, "0" for no daylight
savings time (i.e., winter time) and "1" when daylight savings time
is in effect.
A fatal "time out of range" error will occur if the given time value
is out of range "[0..(~0>>1)]".
If the time value is omitted, the "time()" function is called
instead, internally.
o "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
Localtime([time]);"
This is Date::Calc's equivalent of Perl's built-in "localtime()"
function. See also "localtime" in perlfunc.
The ranges of values returned (and their meanings) are as follows:
$year : 1970..2038 (or more) [Unix etc.]
$year : 1904..2040 [MacOS Classic]
$month : 1..12
$day : 1..31
$hour : 0..23
$min : 0..59
$sec : 0..59
$doy : 1..366
$dow : 1..7
$dst : -1..1
"$doy" is the day of year, sometimes also referred to as the "julian
date", which starts at "1" and goes up to the number of days in that
year.
The day of week ("$dow") will be "1" for Monday, "2" for Tuesday and
so on until "7" for Sunday.
The daylight savings time flag ("$dst") will be ""-1"" if this
information is not available on your system, "0" for no daylight
savings time (i.e., winter time) and "1" when daylight savings time
is in effect.
A fatal "time out of range" error will occur if the given time value
is out of range "[0..(~0>>1)]".
If the time value is omitted, the "time()" function is called
instead, internally.
o "$time = Mktime($year,$month,$day, $hour,$min,$sec);"
This function converts a date into a time value, i.e., into the
number of seconds since whatever moment in time your system considers
to be the "epoch". On Unix and most other systems this is the number
of seconds since January 1st 1970 at midnight (GMT). On MacOS Classic
this is the number of seconds since January 1st 1904 at midnight
(local time).
The function is similar to the "POSIX::mktime()" function (see
"mktime" in POSIX for more details), but in contrast to the latter,
it expects dates in the usual ranges used throughout this module: The
year 2001 stays year 2001, and months are numbered from 1 to 12.
A fatal "date out of range" error will occur if the given date cannot
be expressed in terms of seconds since the epoch (this happens for
instance when the date lies before the epoch, or if it is later than
19-Jan-2038 03:14:07 GMT on 32 bit Unix systems, or later than
06-Feb-2040 06:28:15 (local time) on a Macintosh with MacOS Classic).
Just like the "POSIX::mktime()" function, this function uses the
"mktime()" system call, internally.
This means that the given date and time is considered to be in local
time, and that the value returned by this function will depend on
your machine's local settings such as the time zone, whether daylight
savings time is (or was, at the time) in effect, and the system clock
itself.
BEWARE that "mktime()" does not always return the same time value as
fed into "localtime()", when you feed the output of "localtime()"
back into "mktime()", on some systems!
I.e., ""Mktime((Localtime($time))[0..5])"" will not always return the
same value as given in "$time"!
o "($D_y,$D_m,$D_d, $Dh,$Dm,$Ds, $dst) = Timezone([time]);"
This function returns the difference between ""localtime(time)"" and
""gmtime(time)"", which is the timezone offset in effect for the
current location and the given ""time"".
This offset is positive if you are located to the east of Greenwich,
and is usually negative (except during daylight savings time, in some
locations) if you are located to the west of Greenwich.
Note that this offset is influenced by all of the relevant system
settings and parameters on your machine; such as locales, environment
variables (e.g. ""TZ"") and the system clock itself. See the relevant
documentation on your system for more details.
If the ""time"" is omitted, the ""time()"" function will be called
automatically, internally (similar to the built-in functions
""localtime()"" and ""gmtime()"" in Perl).
A fatal "time out of range" error will occur if the given time value
is out of range "[0..(~0>>1)]".
The last item of the returned list is a flag which indicates whether
daylight savings time is currently in effect. This flag is negative
(-1) if this information is not available on your system. It is zero
(0) when daylight savings time is off, and positive (+1) when
daylight savings time is on.
Thus you can check very quickly whether daylight savings time is
currently in effect by evaluating this function in scalar context (in
scalar context, Perl returns the last item of a list):
if (scalar Timezone > 0) { # yes, daylight savings time
However, a slightly more efficient way would be this:
if (scalar System_Clock > 0) { # yes, daylight savings time
o "$time = Date_to_Time($year,$month,$day, $hour,$min,$sec);"
This function is a replacement for the BSD function "timegm()" (which
is not available on all Unix systems), which converts a given date
and time into a time value, i.e., into the number of seconds since
whatever moment in time your system considers to be the "epoch". On
Unix and most other systems this is the number of seconds since
January 1st 1970 at midnight (GMT). On MacOS Classic this is the
number of seconds since January 1st 1904 at midnight (local time).
Under Unix, the date and time are considered to be in UTC ("Universal
Time Coordinated", and so is the resulting time value.
UTC is almost the same as GMT (or "Greenwich Mean Time"), except that
UTC has leap seconds (in order to account for small variations in the
rotation of the earth, for instance), whereas GMT does not.
Under MacOS Classic, however, both input and output are considered to
be in local time.
The ranges of year and month follow the same rules as throughout the
rest of this module (and not the contorted rules of its Unix
equivalent), i.e., the year "2001" stays "2001" and the month ranges
from 1 to 12.
A fatal "date out of range" error will occur if the given date cannot
be expressed in terms of seconds since the epoch (this happens for
instance when the date lies before the epoch, or if it is later than
19-Jan-2038 03:14:07 GMT on 32 bit Unix systems, or later than
06-Feb-2040 06:28:15 (local time) on a Macintosh with MacOS Classic).
This function should be very fast, because it is implemented in a
very straightforward manner and doesn't use any internal system
calls.
Moreover, the functions "Date_to_Time()" and "Time_to_Date()" are
guaranteed to be complementary, i.e., that
""Date_to_Time(Time_to_Date($time))"" and
""Time_to_Date(Date_to_Time($year,$month,$day, $hour,$min,$sec))""
will always return the initial values.
o "($year,$month,$day, $hour,$min,$sec) = Time_to_Date([time]);"
This function is an alternative to the POSIX "gmtime()" function (and
its built-in Perl equivalent), which converts a given time value into
the corresponding date and time. The given time value must be the
number of seconds since whatever moment in time your system considers
to be the "epoch". On Unix and most other systems this is the number
of seconds since January 1st 1970 at midnight (GMT). On MacOS Classic
this is the number of seconds since January 1st 1904 at midnight
(local time).
Under Unix, the given time value is considered to be in UTC
("Universal Time Coordinated", and so is the resulting date and time.
UTC is almost the same as GMT (or "Greenwich Mean Time"), except that
UTC has leap seconds (in order to account for small variations in the
rotation of the earth, for instance), whereas GMT does not.
Under MacOS Classic, however, both input and output are considered to
be in local time.
If the input value ""time"" is omitted, the ""time()"" function will
be called automatically, internally (similar to the built-in
functions ""localtime()"" and ""gmtime()"" in Perl).
A fatal "time out of range" error will occur if the given time value
is negative.
This function should be very fast, because it is implemented in a
very straightforward manner and doesn't use any internal system calls
(except for "time()", if the input value is omitted).
Moreover, the functions "Date_to_Time()" and "Time_to_Date()" are
guaranteed to be complementary, i.e., that
""Date_to_Time(Time_to_Date($time))"" and
""Time_to_Date(Date_to_Time($year,$month,$day, $hour,$min,$sec))""
will always return the initial values.
o "($year,$month,$day) = Easter_Sunday($year);"
This function calculates the date of Easter Sunday for all years in
the range from 1583 to 2299 (all other year numbers will result in a
fatal "year out of range" error message) using the method known as
the "Gaussian Rule".
Some related christian feast days which depend on the date of Easter
Sunday:
Carnival Monday / Rosenmontag / Veille du Mardi Gras = -48 days
Mardi Gras / Karnevalsdienstag / Mardi Gras = -47 days
Ash Wednesday / Aschermittwoch / Mercredi des Cendres = -46 days
Palm Sunday / Palmsonntag / Dimanche des Rameaux = -7 days
Easter Friday / Karfreitag / Vendredi Saint = -2 days
Easter Saturday / Ostersamstag / Samedi de Paques = -1 day
Easter Monday / Ostermontag / Lundi de Paques = +1 day
Ascension of Christ / Christi Himmelfahrt / Ascension = +39 days
Whitsunday / Pfingstsonntag / Dimanche de Pentecote = +49 days
Whitmonday / Pfingstmontag / Lundi de Pentecote = +50 days
Feast of Corpus Christi / Fronleichnam / Fete-Dieu = +60 days
Use the offsets shown above to calculate the date of the
corresponding feast day as follows:
($year,$month,$day) = Add_Delta_Days(Easter_Sunday($year), $offset));
o "if ($month = Decode_Month($string))"
This function takes a string as its argument, which should contain
the name of a month IN THE CURRENTLY SELECTED LANGUAGE (see further
below for details about the multi-language support of this package),
or any uniquely identifying abbreviation of a month's name (i.e., the
first few letters), and returns the corresponding number (1..12) upon
a successful match, or "0" otherwise (therefore, the return value can
also be used as the conditional expression in an "if" statement).
Note that the input string may not contain any other characters which
do not pertain to the month's name, especially no leading or trailing
whitespace.
Note also that matching is performed in a case-insensitive manner
(this may depend on the "locale" setting on your current system,
though!)
With "English" as the currently selected language (which is the
default), the following examples will all return the value "9":
$month = Decode_Month("s");
$month = Decode_Month("Sep");
$month = Decode_Month("septemb");
$month = Decode_Month("September");
o "if ($dow = Decode_Day_of_Week($string))"
This function takes a string as its argument, which should contain
the name of a day of week IN THE CURRENTLY SELECTED LANGUAGE (see
further below for details about the multi-language support of this
package), or any uniquely identifying abbreviation of the name of a
day of week (i.e., the first few letters), and returns the
corresponding number (1..7) upon a successful match, or "0" otherwise
(therefore, the return value can also be used as the conditional
expression in an "if" statement).
Note that the input string may not contain any other characters which
do not pertain to the name of the day of week, especially no leading
or trailing whitespace.
Note also that matching is performed in a case-insensitive manner
(this may depend on the "locale" setting on your current system,
though!)
With "English" as the currently selected language (which is the
default), the following examples will all return the value "3":
$dow = Decode_Day_of_Week("w");
$dow = Decode_Day_of_Week("Wed");
$dow = Decode_Day_of_Week("wednes");
$dow = Decode_Day_of_Week("Wednesday");
o "if ($lang = Decode_Language($string))"
This function takes a string as its argument, which should contain
the name of one of the languages supported by this package (IN THIS
VERY LANGUAGE ITSELF), or any uniquely identifying abbreviation of
the name of a language (i.e., the first few letters), and returns its
corresponding internal number (1..14 in the original distribution)
upon a successful match, or "0" otherwise (therefore, the return
value can also be used as the conditional expression in an "if"
statement).
Note that the input string may not contain any other characters which
do not pertain to the name of a language, especially no leading or
trailing whitespace.
Note also that matching is performed in a case-insensitive manner
(this may depend on the "locale" setting on your current system,
though!)
The original distribution supports the following thirteen languages:
English ==> 1 (default)
Francais (French) ==> 2
Deutsch (German) ==> 3
Espan~ol (Spanish) ==> 4
Portugues (Portuguese) ==> 5
Nederlands (Dutch) ==> 6
Italiano (Italian) ==> 7
Norsk (Norwegian) ==> 8
Svenska (Swedish) ==> 9
Dansk (Danish) ==> 10
suomi (Finnish) ==> 11
Magyar (Hungarian) ==> 12
polski (Polish) ==> 13
Romaneste (Romanian) ==> 14
See the section "How to install additional languages" in the file
"INSTALL.txt" in this distribution for how to add more languages to
this package.
In the original distribution (no other languages installed), the
following examples will all return the value "3":
$lang = Decode_Language("d");
$lang = Decode_Language("de");
$lang = Decode_Language("Deutsch");
Note that you may not be able to enter the special international
characters in some of the languages' names over the keyboard directly
on some systems.
This should never be a problem, though; just enter an abbreviation of
the name of the language consisting of the first few letters up to
the character before the first special international character.
o "if (($year,$month,$day) = Decode_Date_EU($string))"
This function scans a given string and tries to parse any date which
might be embedded in it.
The function returns an empty list if it can't successfully extract a
valid date from its input string, or else it returns the date found.
The function accepts almost any format, as long as the date is given
in the european order (hence its name) day-month-year.
Thereby, zero or more NON-NUMERIC characters may PRECEDE the day and
FOLLOW the year.
Moreover, zero or more NON-ALPHANUMERIC characters are permitted
BETWEEN these three items (i.e., between day and month and between
month and year).
The month may be given either numerically (i.e., a number from "1" to
"12"), or alphanumerically, i.e., as the name of the month IN THE
CURRENTLY SELECTED LANGUAGE, or any uniquely identifying abbreviation
thereof.
(See further below for details about the multi-language support of
this package!)
If the year is given as one or two digits only (i.e., if the year is
less than 100), it is mapped to a "window" of +/- 50 years around the
current year, as described by the "Moving_Window()" function (see
further below).
If the day, month and year are all given numerically but WITHOUT any
delimiting characters between them, this string of digits will be
mapped to the day, month and year as follows:
Length: Mapping:
3 dmy
4 dmyy
5 dmmyy
6 ddmmyy
7 dmmyyyy
8 ddmmyyyy
(Where "d" stands for "day", "m" stands for "month" and "y" stands
for "year".)
All other strings consisting purely of digits (without any
intervening delimiters) are rejected, i.e., not recognized.
Examples:
"3.1.64"
"3 1 64"
"03.01.64"
"03/01/64"
"3. Jan 1964"
"Birthday: 3. Jan '64 in Backnang/Germany"
"03-Jan-64"
"3.Jan1964"
"3Jan64"
"030164"
"3ja64"
"3164"
Experiment! (See the corresponding example applications in the
"examples" subdirectory of this distribution in order to do so.)
o "if (($year,$month,$day) = Decode_Date_US($string))"
This function scans a given string and tries to parse any date which
might be embedded in it.
The function returns an empty list if it can't successfully extract a
valid date from its input string, or else it returns the date found.
The function accepts almost any format, as long as the date is given
in the U.S. american order (hence its name) month-day-year.
Thereby, zero or more NON-ALPHANUMERIC characters may PRECEDE and
FOLLOW the month (i.e., precede the month and separate it from the
day which follows behind).
Moreover, zero or more NON-NUMERIC characters are permitted BETWEEN
the day and the year, as well as AFTER the year.
The month may be given either numerically (i.e., a number from "1" to
"12"), or alphanumerically, i.e., as the name of the month IN THE
CURRENTLY SELECTED LANGUAGE, or any uniquely identifying abbreviation
thereof.
(See further below for details about the multi-language support of
this package!)
If the year is given as one or two digits only (i.e., if the year is
less than 100), it is mapped to a "window" of +/- 50 years around the
current year, as described by the "Moving_Window()" function (see
further below).
If the month, day and year are all given numerically but WITHOUT any
delimiting characters between them, this string of digits will be
mapped to the month, day and year as follows:
Length: Mapping:
3 mdy
4 mdyy
5 mddyy
6 mmddyy
7 mddyyyy
8 mmddyyyy
(Where "m" stands for "month", "d" stands for "day" and "y" stands
for "year".)
All other strings consisting purely of digits (without any
intervening delimiters) are rejected, i.e., not recognized.
If only the day and the year form a contiguous string of digits, they
will be mapped as follows:
Length: Mapping:
2 dy
3 dyy
4 ddyy
5 dyyyy
6 ddyyyy
(Where "d" stands for "day" and "y" stands for "year".)
Examples:
"1 3 64"
"01/03/64"
"Jan 3 '64"
"Jan 3 1964"
"===> January 3rd 1964 (birthday)"
"Jan31964"
"Jan364"
"ja364"
"1364"
Experiment! (See the corresponding example applications in the
"examples" subdirectory of this distribution in order to do so.)
o "$year = Fixed_Window($yy);"
This function applies a "fixed window" strategy to two-digit year
numbers in order to convert them into four-digit year numbers.
All other year numbers are passed through unchanged, except for
negative year numbers, which cause the function to return zero ("0")
instead.
Two-digit year numbers ""yy"" below 70 are converted to ""20yy"",
whereas year numbers equal to or greater than 70 (but less than 100)
are converted to ""19yy"".
In the original distribution of this package, the base century is set
to "1900" and the base year to "70" (which is a standard on UNIX
systems), but these constants (also called the "epoch") can actually
be chosen at will (in the files "DateCalc.c" and "DateCalc.h") at
compile time of this module.
o "$year = Moving_Window($yy);"
This function applies a "moving window" strategy to two-digit year
numbers in order to convert them into four-digit year numbers,
provided the necessary system calls (system clock) are available.
Otherwise the function falls back to the "fixed window" strategy
described in the function above.
All other year numbers are passed through unchanged, except for
negative year numbers, which cause the function to return zero ("0")
instead.
Two-digit year numbers are mapped according to a "window" of 50 years
in both directions (past and future) around the current year.
That is, two-digit year numbers are first mapped to the same century
as the current year. If the resulting year is smaller than the
current year minus 50, then one more century is added to the result.
If the resulting year is equal to or greater than the current year
plus 50, then a century is subtracted from the result.
o "$date = Compress($year,$month,$day);"
WARNING: This function is legacy code, its use is deprecated!
This function encodes a date in 16 bits, which is the value being
returned.
The encoding scheme is as follows:
Bit number: FEDCBA9 8765 43210
Contents: yyyyyyy mmmm ddddd
(Where the "yyyyyyy" contain the number of the year, "mmmm" the
number of the month and "ddddd" the number of the day.)
The function returns "0" if the given input values do not represent a
valid date. Therefore, the return value of this function can also be
used as the conditional expression in an "if" statement, in order to
check whether the given input values constitute a valid date).
Through this special encoding scheme, it is possible to COMPARE
compressed dates for equality and order (less than/greater than)
WITHOUT any previous DECODING!
Note however that contiguous dates do NOT necessarily have contiguous
compressed representations!
I.e., incrementing the compressed representation of a date MAY OR MAY
NOT yield a valid new date!
Note also that this function can only handle dates within one
century.
This century can be chosen at will (at compile time of this module)
by defining a base century and year (also called the "epoch"). In the
original distribution of this package, the base century is set to
"1900" and the base year to "70" (which is standard on UNIX systems).
This allows this function to handle dates from "1970" up to "2069".
If the given year is equal to, say, "95", this package will
automatically assume that you really meant "1995" instead. However,
if you specify a year number which is SMALLER than 70, like "64", for
instance, this package will assume that you really meant "2064".
You are not confined to two-digit (abbreviated) year numbers, though.
The function also accepts "full-length" year numbers, provided that
they lie in the supported range (i.e., from "1970" to "2069", in the
original configuration of this package).
Note that this function is maintained mainly for backward
compatibility, and that its use is not recommended.
o "if (($century,$year,$month,$day) = Uncompress($date))"
WARNING: This function is legacy code, its use is deprecated!
This function decodes dates that were encoded previously using the
function ""Compress()"".
It returns the century, year, month and day of the date encoded in
"$date" if "$date" represents a valid date, or an empty list
otherwise.
The year returned in "$year" is actually a two-digit year number
(i.e., the year number taken modulo 100), and only the expression
""$century + $year"" yields the "full-length" year number (for
example, "1900 + 95 = 1995").
Note that this function is maintained mainly for backward
compatibility, and that its use is not recommended.
o "if (check_compressed($date))"
WARNING: This function is legacy code, its use is deprecated!
This function returns "true" ("1") if the given input value
constitutes a valid compressed date, and "false" ("0") otherwise.
Note that this function is maintained mainly for backward
compatibility, and that its use is not recommended.
o "$string = Compressed_to_Text($date);"
WARNING: This function is legacy code, its use is deprecated!
This function returns a string of fixed length (always 9 characters
long) containing a textual representation of the compressed date
encoded in "$date".
This string has the form "dd-Mmm-yy", where "dd" is the two-digit
number of the day, "Mmm" are the first three letters of the name of
the month in the currently selected language (see further below for
details about the multi-language support of this package), and "yy"
is the two-digit year number (i.e., the year number taken modulo
100).
If "$date" does not represent a valid date, the string "??-???-??" is
returned instead.
Note that this function is maintained mainly for backward
compatibility, and that its use is not recommended.
o "$string = Date_to_Text($year,$month,$day);"
This function returns a string containing a textual representation of
the given date of the form "www dd-Mmm-yyyy", where "www" are the
first three letters of the name of the day of week in the currently
selected language, or a special abbreviation, if special
abbreviations have been defined for the currently selected language
(see further below for details about the multi-language support of
this package), "dd" is the day (one or two digits), "Mmm" are the
first three letters of the name of the month in the currently
selected language, and "yyyy" is the number of the year in full
length.
If the given input values do not constitute a valid date, a fatal
"not a valid date" error occurs.
(See the section "RECIPES" near the end of this document for a code
snippet for how to print dates in any format you like.)
o "$string = Date_to_Text_Long($year,$month,$day);"
This function returns a string containing a textual representation of
the given date roughly of the form "Wwwwww, dd Mmmmmm yyyy", where
"Wwwwww" is the name of the day of week in the currently selected
language (see further below for details about the multi-language
support of this package), "dd" is the day (one or two digits),
"Mmmmmm" is the name of the month in the currently selected language,
and "yyyy" is the number of the year in full length.
The exact format of the output string depends on the currently
selected language. In the original distribution of this package,
these formats are defined as follows:
1 English : "Wwwwww, Mmmmmm ddth yyyy"
2 French : "Wwwwww dd mmmmmm yyyy"
3 German : "Wwwwww, den dd. Mmmmmm yyyy"
4 Spanish : "Wwwwww, dd de mmmmmm de yyyy"
5 Portuguese : "Wwwwww, dia dd de mmmmmm de yyyy"
6 Dutch : "Wwwwww, dd mmmmmm yyyy"
7 Italian : "Wwwwww, dd Mmmmmm yyyy"
8 Norwegian : "wwwwww, dd. mmmmmm yyyy"
9 Swedish : "wwwwww, dd mmmmmm yyyy"
10 Danish : "wwwwww, dd. mmmmmm yyyy"
11 Finnish : "wwwwww, dd. mmmmmmta yyyy"
12 Hungarian : "dd. Mmmmmm yyyy., wwwwww"
13 Polish : "Wwwwww, dd Mmmmmm yyyy"
14 Romanian : "Wwwwww dd Mmmmmm yyyy"
(You can change these formats in the file "DateCalc.c" before
building this module in order to suit your personal preferences.)
If the given input values do not constitute a valid date, a fatal
"not a valid date" error occurs.
In order to capitalize the day of week at the beginning of the string
in Norwegian, use ""lcfirst(Date_to_Text_Long($year,$month,$day));"".
(See the section "RECIPES" near the end of this document for an
example on how to print dates in any format you like.)
o "$string = English_Ordinal($number);"
This function returns a string containing the (english) abbreviation
of the ordinal number for the given (cardinal) number "$number".
I.e.,
0 => '0th' 10 => '10th' 20 => '20th'
1 => '1st' 11 => '11th' 21 => '21st'
2 => '2nd' 12 => '12th' 22 => '22nd'
3 => '3rd' 13 => '13th' 23 => '23rd'
4 => '4th' 14 => '14th' 24 => '24th'
5 => '5th' 15 => '15th' 25 => '25th'
6 => '6th' 16 => '16th' 26 => '26th'
7 => '7th' 17 => '17th' 27 => '27th'
8 => '8th' 18 => '18th' 28 => '28th'
9 => '9th' 19 => '19th' 29 => '29th'
etc.
o "$string = Calendar($year,$month[,$orthodox]);"
This function returns a calendar of the given month in the given year
(somewhat similar to the UNIX ""cal"" command), IN THE CURRENTLY
SELECTED LANGUAGE (see further below for details about the multi-
language support of this package).
Example:
print Calendar(1998,5);
This will print:
May 1998
Mon Tue Wed Thu Fri Sat Sun
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31
If the optional boolean parameter "$orthodox" is given and true, the
calendar starts on Sunday instead of Monday.
o "$string = Month_to_Text($month);"
This function returns the name of the given month in the currently
selected language (see further below for details about the multi-
language support of this package).
If the given month lies outside of the valid range from "1" to "12",
a fatal "month out of range" error will occur.
o "$string = Day_of_Week_to_Text($dow);"
This function returns the name of the given day of week in the
currently selected language (see further below for details about the
multi-language support of this package).
If the given day of week lies outside of the valid range from "1" to
"7", a fatal "day of week out of range" error will occur.
o "$string = Day_of_Week_Abbreviation($dow);"
This function returns the special abbreviation of the name of the
given day of week, IF such special abbreviations have been defined
for the currently selected language (see further below for details
about the multi-language support of this package).
(In the original distribution of this package, this is only true for
Portuguese.)
If not, the first three letters of the name of the day of week in the
currently selected language are returned instead.
If the given day of week lies outside of the valid range from "1" to
"7", a fatal "day of week out of range" error will occur.
Currently, this table of special abbreviations is only used by the
functions ""Date_to_Text()"" and ""Calendar()"", internally.
o "$string = Language_to_Text($lang);"
This function returns the name of any language supported by this
package when the internal number representing that language is given
as input.
The original distribution supports the following thirteen languages:
1 ==> English (default)
2 ==> Francais (French)
3 ==> Deutsch (German)
4 ==> Espan~ol (Spanish)
5 ==> Portugues (Portuguese)
6 ==> Nederlands (Dutch)
7 ==> Italiano (Italian)
8 ==> Norsk (Norwegian)
9 ==> Svenska (Swedish)
10 ==> Dansk (Danish)
11 ==> suomi (Finnish)
12 ==> Magyar (Hungarian)
13 ==> polski (Polish)
14 ==> Romaneste (Romanian)
See the section "How to install additional languages" in the file
"INSTALL.txt" in this distribution for how to add more languages to
this package.
See the description of the function ""Languages()"" further below to
determine how many languages are actually available in a given
installation of this package.
o "$lang = Language();"
o "Language($lang);"
o "$oldlang = Language($newlang);"
This function can be used to determine which language is currently
selected, and to change the selected language.
Thereby, each language has a unique internal number.
The original distribution contains the following thirteen languages:
1 ==> English (default)
2 ==> Francais (French)
3 ==> Deutsch (German)
4 ==> Espan~ol (Spanish)
5 ==> Portugues (Portuguese)
6 ==> Nederlands (Dutch)
7 ==> Italiano (Italian)
8 ==> Norsk (Norwegian)
9 ==> Svenska (Swedish)
10 ==> Dansk (Danish)
11 ==> suomi (Finnish)
12 ==> Magyar (Hungarian)
13 ==> polski (Polish)
14 ==> Romaneste (Romanian)
See the section "How to install additional languages" in the file
"INSTALL.txt" in this distribution for how to add more languages to
this package.
See the description of the function ""Languages()"" further below to
determine how many languages are actually available in a given
installation of this package.
BEWARE that in order for your programs to be portable, you should
NEVER actually use the internal number of a language in this package
EXPLICITLY, because the same number could mean different languages on
different systems, depending on what languages have been added to any
given installation of this package.
Therefore, you should always use a statement such as
Language(Decode_Language("Name_of_Language"));
to select the desired language, and
$language = Language_to_Text(Language());
or
$old_language = Language_to_Text(Language("Name_of_new_Language"));
to determine the (previously) selected language.
If the so chosen language is not available in the current
installation, this will result in an appropriate error message,
instead of silently using the wrong (a random) language (which just
happens to have the same internal number in the other installation).
Note that in the current implementation of this package, the selected
language is a global setting valid for ALL functions that use the
names of months, days of week or languages internally, valid for ALL
PROCESSES using the same copy of the "Date::Calc" shared library in
memory!
This may have surprising side-effects in a multi-user environment,
and even more so when Perl will be capable of multi-threading in some
future release.
o "$max_lang = Languages();"
This function returns the (maximum) number of languages which are
currently available in your installation of this package.
(This may vary from installation to installation.)
See the section "How to install additional languages" in the file
"INSTALL.txt" in this distribution for how to add more languages to
this package.
In the original distribution of this package there are thirteen
built-in languages, therefore the value returned by this function
will be "14" if no other languages have been added to your particular
installation.
o "if (($year,$month,$day) = Decode_Date_EU2($string))"
This function is the Perl equivalent of the function
""Decode_Date_EU()"" (implemented in C), included here merely as an
example to demonstrate how easy it is to write your own routine in
Perl (using regular expressions) adapted to your own special needs,
should the necessity arise, and intended primarily as a basis for
your own development.
In one particular case this Perl version is actually slightly more
permissive than its C equivalent, as far as the class of permitted
intervening (i.e., delimiting) characters is concerned.
(Can you tell the subtle, almost insignificant difference by looking
at the code? Or by experimenting? Hint: Try the string "a3b1c64d"
with both functions.)
o "if (($year,$month,$day) = Decode_Date_US2($string))"
This function is the Perl equivalent of the function
""Decode_Date_US()"" (implemented in C), included here merely as an
example to demonstrate how easy it is to write your own routine in
Perl (using regular expressions) adapted to your own special needs,
should the necessity arise, and intended primarily as a basis for
your own development.
In one particular case this Perl version is actually slightly more
permissive than its C equivalent.
(Hint: This is the same difference as with the ""Decode_Date_EU()""
and ""Decode_Date_EU2()"" pair of functions.)
In a different case, the C version is a little bit more permissive
than its Perl equivalent.
(Can you tell the difference by looking at the code? Or by
experimenting? Hint: Try the string "(1/364)" with both functions.)
o "if (($year,$month,$day) = Parse_Date($string))"
This function is useful for parsing dates as returned by the UNIX
""date"" command or as found in the headers of e-mail (in order to
determine the date at which some e-mail has been sent or received,
for instance).
Example #1:
($year,$month,$day) = Parse_Date(`/bin/date`);
Example #2:
while (<MAIL>)
{
if (/^From \S/)
{
($year,$month,$day) = Parse_Date($_);
...
}
...
}
The function returns an empty list if it can't extract a valid date
from the input string.
o "$lower = ISO_LC($string);"
Returns a copy of the given string where all letters of the
ISO-Latin-1 character set have been replaced by their lower case
equivalents.
Similar to Perl's built-in function ""lc()"" (see "lc" in perlfunc)
but for the whole ISO-Latin-1 character set, not just plain ASCII.
o "$upper = ISO_UC($string);"
Returns a copy of the given string where all letters of the
ISO-Latin-1 character set have been replaced by their upper case
equivalents.
Similar to Perl's built-in function ""uc()"" (see "uc" in perlfunc)
but for the whole ISO-Latin-1 character set, not just plain ASCII.
o "$string = Date::Calc::Version();"
This function returns a string with the (numeric) version number of
the C library ("DateCalc.c") at the core of this package (which is
also (automatically) the version number of the "Calc.xs" file).
Note that under all normal circumstances, this version number should
be identical with the one found in the Perl variable
"$Date::Calc::VERSION" (the version number of the "Calc.pm" file).
Since this function is not exported, you always have to qualify it
explicitly, i.e., ""Date::Calc::Version()"".
This is to avoid possible name space conflicts with version functions
from other modules.
RECIPES
1) How do I compare two dates?
Solution #1:
use Date::Calc qw( Date_to_Days );
if (Date_to_Days($year1,$month1,$day1) <
Date_to_Days($year2,$month2,$day2))
if (Date_to_Days($year1,$month1,$day1) <=
Date_to_Days($year2,$month2,$day2))
if (Date_to_Days($year1,$month1,$day1) >
Date_to_Days($year2,$month2,$day2))
if (Date_to_Days($year1,$month1,$day1) >=
Date_to_Days($year2,$month2,$day2))
if (Date_to_Days($year1,$month1,$day1) ==
Date_to_Days($year2,$month2,$day2))
if (Date_to_Days($year1,$month1,$day1) !=
Date_to_Days($year2,$month2,$day2))
$cmp = (Date_to_Days($year1,$month1,$day1) <=>
Date_to_Days($year2,$month2,$day2));
Solution #2:
use Date::Calc qw( Delta_Days );
if (Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2) > 0)
if (Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2) >= 0)
if (Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2) < 0)
if (Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2) <= 0)
if (Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2) == 0)
if (Delta_Days($year1,$month1,$day1,
$year2,$month2,$day2) != 0)
2) How do I check whether a given date lies within a certain range of
dates?
use Date::Calc qw( Date_to_Days );
$lower = Date_to_Days($year1,$month1,$day1);
$upper = Date_to_Days($year2,$month2,$day2);
$date = Date_to_Days($year,$month,$day);
if (($date >= $lower) && ($date <= $upper))
{
# ok
}
else
{
# not ok
}
3) How do I compare two dates with times? How do I check whether two
dates and times lie more or less than a given time interval apart?
Solution #1:
use Date::Calc qw( Add_Delta_DHMS Date_to_Days );
@date1 = (2002,8,31,23,59,1);
@date2 = (2002,9,1,11,30,59); # ==> less than 12 hours
#@date1 = (2002,8,31,22,59,1);
#@date2 = (2002,9,1,11,30,59); # ==> more than 12 hours
# Omit the next line if you just want to compare the two dates
# (and change @date3 and @d3 to @date1 and @d1, respectively):
@date3 = Add_Delta_DHMS(@date1, 0,12,0,0); # ==> is the difference within 12 hours?
@d2 = ( Date_to_Days(@date2[0..2]), ($date2[3]*60+$date2[4])*60+$date2[5] );
@d3 = ( Date_to_Days(@date3[0..2]), ($date3[3]*60+$date3[4])*60+$date3[5] );
@diff = ( $d2[0]-$d3[0], $d2[1]-$d3[1] );
if ($diff[0] > 0 and $diff[1] < 0) { $diff[0]--; $diff[1] += 86400; }
if ($diff[0] < 0 and $diff[1] > 0) { $diff[0]++; $diff[1] -= 86400; }
if (($diff[0] || $diff[1]) >= 0) { print "More than 12 hours.\n"; }
else { print "Less than 12 hours.\n"; }
Solution #2:
This solution is only feasible if your dates are guaranteed to lie
within the range given by your system's epoch and overflow date and
time!
Unix: 1-Jan-1970 00:00:00 to 19-Jan-2038 03:14:07
MacOS: 1-Jan-1904 00:00:00 to 6-Feb-2040 06:28:15
use Date::Calc qw( Date_to_Time );
@date1 = (2002,8,31,23,59,1);
@date2 = (2002,9,1,11,30,59); # ==> less than 12 hours
#@date1 = (2002,8,31,22,59,1);
#@date2 = (2002,9,1,11,30,59); # ==> more than 12 hours
$d1 = Date_to_Time(@date1);
$d2 = Date_to_Time(@date2);
if ($d1 <= $d2) { print "The two dates are in chronological order.\n"; }
else { print "The two dates are in reversed order.\n"; }
if ($d1 + 12*60*60 <= $d2) { print "More than 12 hours.\n"; }
else { print "Less than 12 hours.\n"; }
4) How do I verify whether someone has a certain age?
use Date::Calc qw( Decode_Date_EU Today leap_year Delta_Days );
$date = <STDIN>; # get birthday
($year1,$month1,$day1) = Decode_Date_EU($date);
($year2,$month2,$day2) = Today();
if (($day1 == 29) && ($month1 == 2) && !leap_year($year2))
{ $day1--; }
if ( (($year2 - $year1) > 18) ||
( (($year2 - $year1) == 18) &&
(Delta_Days($year2,$month1,$day1, $year2,$month2,$day2) >= 0) ) )
{
print "Ok - you are over 18.\n";
}
else
{
print "Sorry - you aren't 18 yet!\n";
}
Or, alternatively (substituting the last "if" statement above):
if (($year1+18 <=> $year2 || $month1 <=> $month2 || $day1 <=> $day2) <= 0)
{ print "Ok - you are over 18.\n"; }
else
{ print "Sorry - you aren't 18 yet!\n"; }
5) How do I calculate the number of the week of month the current date
lies in?
For example:
April 1998
Mon Tue Wed Thu Fri Sat Sun
1 2 3 4 5 = week #1
6 7 8 9 10 11 12 = week #2
13 14 15 16 17 18 19 = week #3
20 21 22 23 24 25 26 = week #4
27 28 29 30 = week #5
Solution:
use Date::Calc qw( Today Day_of_Week );
($year,$month,$day) = Today();
$week = int(($day + Day_of_Week($year,$month,1) - 2) / 7) + 1;
6) How do I calculate whether a given date is the 1st, 2nd, 3rd, 4th
or 5th of that day of week in the given month?
For example:
October 2000
Mon Tue Wed Thu Fri Sat Sun
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31
Is Sunday, the 15th of October 2000, the 1st, 2nd, 3rd, 4th or 5th
Sunday of that month?
Solution:
use Date::Calc qw( Day_of_Week Delta_Days
Nth_Weekday_of_Month_Year
Date_to_Text_Long English_Ordinal
Day_of_Week_to_Text Month_to_Text );
($year,$month,$day) = (2000,10,15);
$dow = Day_of_Week($year,$month,$day);
$n = int( Delta_Days(
Nth_Weekday_of_Month_Year($year,$month,$dow,1),
$year,$month,$day)
/ 7) + 1;
printf("%s is the %s %s in %s %d.\n",
Date_to_Text_Long($year,$month,$day),
English_Ordinal($n),
Day_of_Week_to_Text($dow),
Month_to_Text($month),
$year);
This prints:
Sunday, October 15th 2000 is the 3rd Sunday in October 2000.
7) How do I calculate the date of the Wednesday of the same week as
the current date?
Solution #1:
use Date::Calc qw( Today Day_of_Week Add_Delta_Days );
$searching_dow = 3; # 3 = Wednesday
@today = Today();
$current_dow = Day_of_Week(@today);
@date = Add_Delta_Days(@today, $searching_dow - $current_dow);
Solution #2:
use Date::Calc qw( Today Add_Delta_Days
Monday_of_Week Week_of_Year );
$searching_dow = 3; # 3 = Wednesday
@today = Today();
@date = Add_Delta_Days( Monday_of_Week( Week_of_Year(@today) ),
$searching_dow - 1 );
Solution #3:
use Date::Calc qw( Standard_to_Business Today
Business_to_Standard );
@business = Standard_to_Business(Today());
$business[2] = 3; # 3 = Wednesday
@date = Business_to_Standard(@business);
8) How can I add a week offset to a business date (including across
year boundaries)?
use Date::Calc qw( Business_to_Standard Add_Delta_Days
Standard_to_Business );
@temp = Business_to_Standard($year,$week,$dow);
@temp = Add_Delta_Days(@temp, $week_offset * 7);
($year,$week,$dow) = Standard_to_Business(@temp);
9) How do I calculate the last and the next Saturday for any given
date?
use Date::Calc qw( Today Day_of_Week Add_Delta_Days
Day_of_Week_to_Text Date_to_Text );
$searching_dow = 6; # 6 = Saturday
@today = Today();
$current_dow = Day_of_Week(@today);
if ($searching_dow == $current_dow)
{
@prev = Add_Delta_Days(@today,-7);
@next = Add_Delta_Days(@today,+7);
}
else
{
if ($searching_dow > $current_dow)
{
@next = Add_Delta_Days(@today,
$searching_dow - $current_dow);
@prev = Add_Delta_Days(@next,-7);
}
else
{
@prev = Add_Delta_Days(@today,
$searching_dow - $current_dow);
@next = Add_Delta_Days(@prev,+7);
}
}
$dow = Day_of_Week_to_Text($searching_dow);
print "Today is: ", ' ' x length($dow),
Date_to_Text(@today), "\n";
print "Last $dow was: ", Date_to_Text(@prev), "\n";
print "Next $dow will be: ", Date_to_Text(@next), "\n";
This will print something like:
Today is: Sun 12-Apr-1998
Last Saturday was: Sat 11-Apr-1998
Next Saturday will be: Sat 18-Apr-1998
10) How can I calculate the last business day (payday!) of a month?
Solution #1 (holidays NOT taken into account):
use Date::Calc qw( Days_in_Month Day_of_Week Add_Delta_Days );
$day = Days_in_Month($year,$month);
$dow = Day_of_Week($year,$month,$day);
if ($dow > 5)
{
($year,$month,$day) =
Add_Delta_Days($year,$month,$day, 5-$dow);
}
Solution #2 (holidays taken into account):
This solution expects a multi-dimensional array "@holiday", which
contains all holidays, as follows: ""$holiday[$year][$month][$day]
= 1;"".
(See the description of the function ""Easter_Sunday()"" further
above for how to calculate the moving (variable) christian feast
days!)
Days which are not holidays remain undefined or should have a value
of zero in this array.
use Date::Calc qw( Days_in_Month Add_Delta_Days Day_of_Week );
$day = Days_in_Month($year,$month);
while (1)
{
while ($holiday[$year][$month][$day])
{
($year,$month,$day) =
Add_Delta_Days($year,$month,$day, -1);
}
$dow = Day_of_Week($year,$month,$day);
if ($dow > 5)
{
($year,$month,$day) =
Add_Delta_Days($year,$month,$day, 5-$dow);
}
else { last; }
}
Solution #3 (holidays taken into account, more comfortable, but
requires Date::Calendar(3) and Date::Calc::Object(3)):
use Date::Calc::Object qw( Today Add_Delta_YM Date_to_Text_Long );
use Date::Calendar::Profiles qw($Profiles);
use Date::Calendar;
$calendar = Date::Calendar->new( $Profiles->{'DE-BW'} );
@today = Today();
@nextmonth = Add_Delta_YM(@today[0,1],1, 0,1);
$workaround = $calendar->add_delta_workdays(@nextmonth,+1);
$payday = $calendar->add_delta_workdays($workaround,-2);
print "Pay day = ", Date_to_Text_Long($payday->date()), "\n";
The "workaround" is necessary due to a bug in the method
"add_delta_workdays()" when adding a negative number of workdays.
11) How do I convert a MS Visual Basic "DATETIME" value into its date
and time constituents?
use Date::Calc qw( Add_Delta_DHMS Date_to_Text );
$datetime = "35883.121653";
($Dd,$Dh,$Dm,$Ds) = ($datetime =~ /^(\d+)\.(\d\d)(\d\d)(\d\d)$/);
($year,$month,$day, $hour,$min,$sec) =
Add_Delta_DHMS(1900,1,1, 0,0,0, $Dd,$Dh,$Dm,$Ds);
printf("The given date is %s %02d:%02d:%02d\n",
Date_to_Text($year,$month,$day), $hour, $min, $sec);
This prints:
The given date is Tue 31-Mar-1998 12:16:53
Since I do not have or use Visual Basic, I can't guarantee that the
number format assumed here is really the one used by Visual Basic -
but you get the general idea. ":-)"
Moreover, consider the following:
Morten Sickel <Morten.Sickel@nrpa.no> wrote:
I discovered a bug in Excel (2000): Excel thinks that 1900 was a
leap year. Users should use 31-Dec-1899 as the date to add an Excel
date value to in order to get the correct date.
I found out on the web that this bug originated in Lotus 123, which
made 29-Feb-1900 an "industrial standard". MS chose to keep the bug
in order to be compatible with Lotus 123. But they have not
mentioned anything about it in the help files.
12) How can I send a reminder to members of a group on the day before a
meeting which occurs every first Friday of a month?
use Date::Calc qw( Today Date_to_Days Add_Delta_YMD
Nth_Weekday_of_Month_Year );
($year,$month,$day) = Today();
$tomorrow = Date_to_Days($year,$month,$day) + 1;
$dow = 5; # 5 = Friday
$n = 1; # 1 = First of that day of week
$meeting_this_month = Date_to_Days(
Nth_Weekday_of_Month_Year($year,$month,$dow,$n) );
($year,$month,$day) = Add_Delta_YMD($year,$month,$day, 0,1,0);
$meeting_next_month = Date_to_Days(
Nth_Weekday_of_Month_Year($year,$month,$dow,$n) );
if (($tomorrow == $meeting_this_month) ||
($tomorrow == $meeting_next_month))
{
# Send reminder e-mail!
}
13) How can I print a date in a different format than provided by the
functions ""Date_to_Text()"", ""Date_to_Text_Long()"" or
""Compressed_to_Text()""?
use Date::Calc qw( Today Day_of_Week_to_Text
Day_of_Week Month_to_Text
English_Ordinal );
($year,$month,$day) = Today();
For example with leading zeros for the day: "Fri 03-Jan-1964"
printf("%.3s %02d-%.3s-%d\n",
Day_of_Week_to_Text(Day_of_Week($year,$month,$day)),
$day,
Month_to_Text($month),
$year);
For example in U.S. american format: "April 12th, 1998"
$string = sprintf("%s %s, %d",
Month_to_Text($month),
English_Ordinal($day),
$year);
For example in one of the possible formats as specified by
ISO 8601:
@date = ($year,$month,$day,$hour,$min,$sec);
$date = sprintf("%d-%02d-%02d %02d:%02d:%02d", @date);
(See also "printf" in perlfunc(1) and/or "sprintf" in perlfunc(1)!)
14) How can I iterate through a range of dates?
use Date::Calc qw( Delta_Days Add_Delta_Days );
@start = (1999,5,27);
@stop = (1999,6,1);
$j = Delta_Days(@start,@stop);
for ( $i = 0; $i <= $j; $i++ )
{
@date = Add_Delta_Days(@start,$i);
printf("%4d/%02d/%02d\n", @date);
}
Note that the loop can be improved; see also the recipe below.
15) How can I create a (Perl) list of dates in a certain range?
use Date::Calc qw( Delta_Days Add_Delta_Days Date_to_Text );
sub date_range
{
my(@date) = (@_)[0,1,2];
my(@list);
my($i);
$i = Delta_Days(@_);
while ($i-- >= 0)
{
push( @list, [ @date ] );
@date = Add_Delta_Days(@date, 1) if ($i >= 0);
}
return(@list);
}
@range = &date_range(1999,11,3, 1999,12,24); # in chronological order
foreach $date (@range)
{
print Date_to_Text(@{$date}), "\n";
}
Note that you probably shouldn't use this one, because it is much
more efficient to iterate through all the dates (as shown in the
recipe immediately above) than to construct such an array and then
to loop through it. Also, it is much more space-efficient not to
create this array.
16) How can I calculate the difference in days between dates, but
without counting Saturdays and Sundays?
sub Delta_Business_Days
{
my(@date1) = (@_)[0,1,2];
my(@date2) = (@_)[3,4,5];
my($minus,$result,$dow1,$dow2,$diff,$temp);
$minus = 0;
$result = Delta_Days(@date1,@date2);
if ($result != 0)
{
if ($result < 0)
{
$minus = 1;
$result = -$result;
$dow1 = Day_of_Week(@date2);
$dow2 = Day_of_Week(@date1);
}
else
{
$dow1 = Day_of_Week(@date1);
$dow2 = Day_of_Week(@date2);
}
$diff = $dow2 - $dow1;
$temp = $result;
if ($diff != 0)
{
if ($diff < 0)
{
$diff += 7;
}
$temp -= $diff;
$dow1 += $diff;
if ($dow1 > 6)
{
$result--;
if ($dow1 > 7)
{
$result--;
}
}
}
if ($temp != 0)
{
$temp /= 7;
$result -= ($temp << 1);
}
}
if ($minus) { return -$result; }
else { return $result; }
}
This solution is probably of little practical value, however,
because it doesn't take legal holidays into account.
See Date::Calendar(3) for how to do that.
17) How can I "normalize" the output of the "Delta_YMDHMS()" (or
"Delta_YMD()") function so that it contains only positive values?
I.e., how can I show a difference in date (and time) in a more
human-readable form, for example in order to show how much time
until (or since) the expiration of something (e.g. an account, a
domain, a credit card, etc.) is left (has passed)?
a) Delta_YMDHMS():
#!perl
use strict;
use Date::Calc qw(Today_and_Now Delta_YMDHMS Add_Delta_YMDHMS Delta_DHMS Date_to_Text);
my $today = [Today_and_Now()];
my $target = [2005,1,1,0,0,0];
my $sign = "until";
my $delta = Normalize_Delta_YMDHMS($today,$target);
if ($delta->[0] < 0)
{
$sign = "since";
$delta = Normalize_Delta_YMDHMS($target,$today);
}
printf("Today is %s %02d:%02d:%02d\n", Date_to_Text(@{$today}[0..2]), @{$today}[3..5]);
printf
(
"%d year%s, %d month%s, %d day%s, %d hour%s, %d minute%s, %d second%s %s %s %02d:%02d:%02d\n",
$delta->[0], (($delta->[0]==1)?'':'s'),
$delta->[1], (($delta->[1]==1)?'':'s'),
$delta->[2], (($delta->[2]==1)?'':'s'),
$delta->[3], (($delta->[3]==1)?'':'s'),
$delta->[4], (($delta->[4]==1)?'':'s'),
$delta->[5], (($delta->[5]==1)?'':'s'),
$sign,
Date_to_Text(@{$target}[0..2]),
@{$target}[3..5]
);
sub Normalize_Delta_YMDHMS
{
my($date1,$date2) = @_;
my(@delta);
@delta = Delta_YMDHMS(@$date1,@$date2);
while ($delta[1] < 0 or
$delta[2] < 0 or
$delta[3] < 0 or
$delta[4] < 0 or
$delta[5] < 0)
{
if ($delta[1] < 0) { $delta[0]--; $delta[1] += 12; }
if ($delta[2] < 0)
{
$delta[1]--;
@delta[2..5] = (0,0,0,0);
@delta[2..5] = Delta_DHMS(Add_Delta_YMDHMS(@$date1,@delta),@$date2);
}
if ($delta[3] < 0) { $delta[2]--; $delta[3] += 24; }
if ($delta[4] < 0) { $delta[3]--; $delta[4] += 60; }
if ($delta[5] < 0) { $delta[4]--; $delta[5] += 60; }
}
return \@delta;
}
b) Delta_YMD():
#!perl
use strict;
use Date::Calc qw(Today Delta_YMD Add_Delta_YM Delta_Days Date_to_Text);
my($sign,$delta);
my $today = [Today()];
my $target = [2005,1,1];
if (Delta_Days(@$today,@$target) < 0)
{
$sign = "since";
$delta = Normalize_Delta_YMD($target,$today);
}
else
{
$sign = "until";
$delta = Normalize_Delta_YMD($today,$target);
}
print "Today is ", Date_to_Text(@$today), "\n";
printf
(
"%d year%s, %d month%s, %d day%s %s %s\n",
$delta->[0], (($delta->[0]==1)?'':'s'),
$delta->[1], (($delta->[1]==1)?'':'s'),
$delta->[2], (($delta->[2]==1)?'':'s'),
$sign,
Date_to_Text(@$target)
);
sub Normalize_Delta_YMD
{
my($date1,$date2) = @_;
my(@delta);
@delta = Delta_YMD(@$date1,@$date2);
while ($delta[1] < 0 or $delta[2] < 0)
{
if ($delta[1] < 0) { $delta[0]--; $delta[1] += 12; }
if ($delta[2] < 0)
{
$delta[1]--;
$delta[2] = Delta_Days(Add_Delta_YM(@$date1,@delta[0,1]),@$date2);
}
}
return \@delta;
}
Note that for normalizing just a time vector, you can use the
built-in function "Normalize_DHMS()". However, this will yield
either all positive OR all negative values, NOT all positive values
as above.
SEE ALSO
Date::Calc::Object(3), Date::Calendar(3), Date::Calendar::Year(3),
Date::Calendar::Profiles(3).
"The Calendar FAQ":
http://www.tondering.dk/claus/calendar.html
by Claus Tondering <claus@tondering.dk>
LIMITATIONS
In the current implementation of this package, the selected language is
stored in a global variable.
Therefore, when you are using a threaded Perl, this may cause undesired
side effects (of one thread always selecting the language for ALL OTHER
threads as well).
VERSION
This man page documents "Date::Calc" version 5.4.
AUTHOR
Steffen Beyer
mailto:sb@engelschall.com
http://www.engelschall.com/u/sb/download/
COPYRIGHT
Copyright (c) 1995 - 2004 by Steffen Beyer. All rights reserved.
LICENSE
This package is free software; you can redistribute it and/or modify it
under the same terms as Perl itself, i.e., under the terms of the
"Artistic License" or the "GNU General Public License".
The C library at the core of this Perl module can additionally be
redistributed and/or modified under the terms of the "GNU Library
General Public License".
Please refer to the files "Artistic.txt", "GNU_GPL.txt" and
"GNU_LGPL.txt" in this distribution for details!
DISCLAIMER
This package is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the "GNU General Public License" for more details.
perl v5.10.0 2004-10-03 Calc(3)
Mac OS X 10.6 - Generated Thu Sep 17 20:11:33 CDT 2009