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/down
load/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) -- actu
ally all year numbers from 1 to the largest positive inte
ger representable on your system (which is at least 32767)
can be dealt with.

(This is not true 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 range from 01-Jan-1970 00:00:00 GMT to
19-Jan-2038 03:14:07 GMT.)

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 by most (not all) Euro
pean countries, in obedience to the corresponding decree
of catholic pope Gregor I 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 par
ticular 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);
Week_of_Year
    ($week,$year) = Week_of_Year($year,$month,$day);
    $week  =  Week_of_Year($year,$month,$day); # BEWARE!
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!)

� "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 Gregor I!; 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 con
tain 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 includ
ing 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 some what ":-)" on 64 bit systems).
Note further that the function "Easter_Sunday()" can only be used for years in the range 1583 to 2299.
� 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 lan
guage 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 actu
ally lies in the last week of the PREVIOUS year.
� Function naming conventions: Function names completely in lower case indicate a
boolean return value.
� Boolean values: Boolean values in this module are always a numeric zero
("0") for "false" and a numeric one ("1") for "true".
� 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 your
self by enclosing the function call in an ""eval"" with
curly brackets and checking the special variable "$@"
(see "eval" in perlfunc(1) for details).

DESCRIPTION

� "use Date::Calc qw( Days_in_Year Days_in_Month ... );"

� "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.
� "$days = Days_in_Year($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 "$year", i.e., either "365" or
"366".
� "$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.
� "$weeks = Weeks_in_Year($year);": This function returns the number of weeks in the given
year "$year", i.e., either "52" or "53".
� "if (leap_year($year))": This function returns "true" ("1") if the given year
"$year" is a leap year and "false" ("0") otherwise.
� "if (check_date($year,$month,$day))": This function returns "true" ("1") if the given three
numerical values "$year", "$month" and "$day" constitute
a valid date, and "false" ("0") otherwise.
� "if (check_time($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
<= $sec < 60"), and "false" ("0") otherwise.
� "if (check_business_date($year,$week,$dow))": This function returns "true" ("1") if the given three
numerical values "$year", "$week" and "$dow" constitute
a valid date in business format, and "false" ("0") oth
erwise.; Beware that this function does NOT compute whether a given date is a business day (i.e., Monday to Friday)!; To do so, use ""(Day_of_Week($year,$month,$day) < 6)""
instead.
� "$doy = Day_of_Year($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($year,12,31)"" returns either "365" or
"366".
� "$days = Date_to_Days($year,$month,$day);": This function returns the (absolute) number of the day
of the given date, where counting starts at the 1st of
January of the year 1 A.D.; I.e., ""Date_to_Days(1,1,1)"" returns "1",
""Date_to_Days(1,12,31)"" returns "365",
""Date_to_Days(2,1,1)"" returns "366",
""Date_to_Days(1998,5,1)"" returns "729510", and so on.
� "$dow = Day_of_Week($year,$month,$day);": This function returns the number of the day of week of
the given date.; The function returns "1" for Monday, "2" for Tuesday and
so on until "7" for Sunday.; Note that in the Hebrew calendar (on which the Christian
calendar is based), the week starts with Sunday and ends
with the Sabbath or Saturday (where according to the
Genesis (as described in the Bible) the Lord rested from
creating the world).; In medieval times, catholic popes have decreed the Sun
day to be the official day of rest, in order to dissoci
ate the Christian from the Hebrew belief.; Nowadays, the Sunday AND the Saturday are commonly con
sidered (and used as) days of rest, usually referred to
as the "week-end".; Consistent with this practice, current norms and stan
dards (such as ISO/R 2015-1971, DIN 1355 and ISO 8601)
define the Monday as the first day of the week.
� "$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.
� "($week,$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), $year)""
is returned.
� "$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,$day);"" (note the parenthe
ses around "$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 your
self.; In case you do not understand this, never mind, but then
simply DO NOT USE this function in scalar context!
� "($year,$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,$day) = Mon
day_of_Week(Week_of_Year($year,$month,$day));"" in order
to calculate the date of the Monday of the same week as
the given date.
� "if (($year,$month,$day) = Nth_Week: day_of_Month_Year($year,$month,$dow,$n))"; This function calculates the date of the "$n"th day of
week "$dow" in the given month "$month" and year
"$year"; such as, for example, the 3rd Thursday of a
given month and year.; This can be used to send a notification mail to the mem
bers of a group which meets regularly on every 3rd
Thursday of a month, for instance.; (See the section "RECIPES" near the end of this document
for a code snippet to actually do so.); "$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 "$n" must lie in the range "1"
to "5", or a fatal error (with appropriate error mes
sage) occurs.; The function returns an empty list when the 5th of a
given day of week does not exist in the given month and
year.
� "($year,$week,$dow) = Standard_to_Busi: ness($year,$month,$day);"; This function converts a given date from standard nota
tion (year, month, day (of month)) to business notation
(year, week, day of week).
� "($year,$month,$day) = Business_to_Stan: dard($year,$week,$dow);"; This function converts a given date from business nota
tion (year, week, day of week) to standard notation
(year, month, day (of month)).
� "$Dd = Delta_Days($year1,$month1,$day1,: $year2,$month2,$day2);"; This function returns the difference in days between the
two given dates.; The result is positive if the two dates are in chrono
logical order, i.e., if date #1 comes chronologically
BEFORE date #2, and negative if the order of the two
dates is reversed.; The result is zero if the two dates are identical.
� "($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.; � "($Dy,$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.; � "($D_y,$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.; � "($Dd,$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.; � "($year,$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 repre
sentation 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 "$delta" again.; � "($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);

� "($year,$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!).

� "($year,$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 transfor
mation 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 func
tions ""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,-$Dd);
will in general NOT return the initial date "@date".
Note that this is NOT a program bug but NECESSARILY so because of the variable lengths of years and months!
� "($year,$month,$day, $hour,$min,$sec) =: Add_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec,
$D_y,$D_m,$D_d, $Dh,$Dm,$Ds);"; Same as the function above, except that a time offset
may be given in addition to the year, month and day off
set.
� "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =: System_Clock([$gmt]);"; If your operating system supports the corresponding sys
tem 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)
$month : 1..12
$day : 1..31
$hour : 0..23
$min : 0..59
$sec : 0..59 (0..61 on some sys

tems)
$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 informa

tion 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 "$gmt" is given, a "true" value ("1") will cause ""gmtime()"" to be used instead of ""localtime()"", internally, thus returning Greenwich Mean Time (GMT, or UTC) instead of local time.
� "($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.
� "($hour,$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 sec
onds).; 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 "$gmt" is
given, a "true" value ("1") will cause ""gmtime()"" to
be used instead of ""localtime()"", internally, thus
returning Greenwich Mean Time (GMT, or UTC) instead of
local time.
� "($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 "$gmt" is
given, a "true" value ("1") will cause ""gmtime()"" to
be used instead of ""localtime()"", internally, thus
returning Greenwich Mean Time (GMT, or UTC) instead of
local time.
� "$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).
� "($year,$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)
$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.
� "($year,$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 perl func.; The ranges of values returned (and their meanings) are
as follows:

$year : 1970..2038 (or more)
$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.
� "$time = Mktime($year,$month,$day, $hour,$min,$sec);": This function converts a date into a Unix time value
(i.e., the number of seconds since January 1st 1970 at
midnight, which is also called the "epoch").; The function is similar to the "POSIX::mktime()" func tion (see "mktime" in POSIX for more details), but in
contrast to the latter, it expects dates in the usual
ranges used throughout this module: The year 2001 stays
year 2001, and months are numbered from 1 to 12.; A fatal "date out of range" error will occur if the
given date cannot be expressed in terms of seconds since
the epoch (this happens for instance when the date lies
before the epoch, or if it is later than
19-Jan-2038 03:14:07 GMT on 32 bit systems).; Just like the "POSIX::mktime()" function, this function uses the "mktime()" system call, internally.; This means that the given date and time is considered to
be in local time, and that the value returned by this
function will depend on your machine's local settings
such as the time zone, whether daylight savings time is
(or was, at the time) in effect, and the system clock
itself.; BEWARE that "mktime()" does not always return the same time value as fed into "localtime()", when you feed the output of "localtime()" into "mktime()", on some sys tems!; I.e., ""Mktime((Localtime($time))[0..5])"" will not
always return the same value as given in "$time"!
� "($D_y,$D_m,$D_d, $Dh,$Dm,$Ds, $dst) = Time: zone([time]);"; This function returns the difference between ""local
time(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 (lest during day
light savings time, in some locations) if you are
located to the west of Greenwich.; Note that this offset is influenced by all of the rele
vant 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 indi
cates 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; � "$time = Date_to_Time($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 Unix time
value (i.e., the number of seconds since January 1st
1970 at midnight, the latter of which is called the
"epoch").

The date and time are considered to be in UTC ("Univer
sal Time Coordinated", this is the same as GMT or
"Greenwich Mean Time"), and so is the resulting time
value.

The ranges of year and month follow the same rules as
throughout the rest of this module (and not the con
torted 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).

This function should be very fast, because it is imple
mented 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,$sec))"" will always return the initial val
ues.; � "($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 con
verts a given Unix time value (i.e., the number of sec
onds since the epoch, that is, since January 1st 1970 at
midnight) into the corresponding date and time.

The given time value is considered to be in UTC ("Uni
versal Time Coordinated", which is the same a GMT,
"Greenwich Mean Time"), and so is the resulting date and
time.

If the input value ""time"" is omitted, the ""time()""
function will be called automatically, internally (simi
lar 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 imple
mented 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,$sec))"" will always return the initial val
ues.; � "($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_Sun

day($year), $offset));

� "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 corre
sponding 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-insensi
tive 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");

� "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 CUR
RENTLY 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" state
ment).

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-insensi
tive 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");

� "if ($lang = Decode_Language($string))"

This function takes a string as its argument, which
should contain the name of one of the languages sup
ported 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..11 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 lan
guage, especially no leading or trailing whitespace.

Note also that matching is performed in a case-insensi
tive manner (this may depend on the "locale" setting on
your current system, though!)

The original distribution supports the following eleven
languages:

English ==> 1 (de

fault)
Fran�ais (French) ==> 2
Deutsch (German) ==> 3
Espa�ol (Spanish) ==> 4
Portugu�s (Portuguese) ==> 5
Nederlands (Dutch) ==> 6
Italiano (Italian) ==> 7
Norsk (Norwegian) ==> 8
Svenska (Swedish) ==> 9
Dansk (Danish) ==> 10
suomi (Finnish) ==> 11
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");
$lang = Decode_Language("Deutsch");
Note that you may not be able to enter the special international characters in some of the languages' names over the keyboard directly on some systems.
This should never be a problem, though; just enter an abbreviation of the name of the language consisting of the first few letters up to the character before the first special international character.
� "if (($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 success
fully 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 num
ber 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 rec ognized.
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.)
� "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 success
fully 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 per mitted BETWEEN the day and the year, as well as AFTER the year.; The month may be given either numerically (i.e., a num
ber 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 rec ognized.
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.)
� "$year = Fixed_Window($yy);": This function applies a "fixed window" strategy to twodigit year numbers in order to convert them into fourdigit year numbers.; All other year numbers are passed through unchanged,
except for negative year numbers, which cause the func
tion 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 con
stants (also called the "epoch") can actually be chosen
at will (in the files "DateCalc.c" and "DateCalc.h") at
compile time of this module.
� "$year = Moving_Window($yy);": This function applies a "moving window" strategy to twodigit year numbers in order to convert them into fourdigit 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 func
tion to return zero ("0") instead.; Two-digit year numbers are mapped according to a "win
dow" 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.
� "$date = Compress($year,$month,$day);": WARNING: This function is legacy code, its use is depre
cated!; 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 back ward compatibility, and that its use is not recommended.
� "if (($century,$year,$month,$day) = Uncompress($date))": WARNING: This function is legacy code, its use is depre
cated!; This function decodes dates that were encoded previously
using the function ""Compress()"".; It returns the century, year, month and day of the date
encoded in "$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 + $year"" yields the
"full-length" year number (for example, "1900 + 95 =
1995").; Note that this function is maintained mainly for back
ward compatibility, and that its use is not recommended.
� "if (check_compressed($date))": WARNING: This function is legacy code, its use is depre
cated!; 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 back
ward compatibility, and that its use is not recommended.
� "$string = Compressed_to_Text($date);": WARNING: This function is legacy code, its use is depre
cated!; 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 back
ward compatibility, and that its use is not recommended.
� "$string = Date_to_Text($year,$month,$day);": This function returns a string containing a textual rep
resentation 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 abbrevi
ations have been defined for the currently selected lan
guage (see further below for details about the multilanguage 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.)
� "$string = Date_to_Text_Long($year,$month,$day);": This function returns a string containing a textual rep
resentation 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 sup
port of this package), "dd" is the day (one or two dig
its), "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 distribu
tion of this package, these formats are defined as fol
lows:

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"
(You can change these formats in the file "DateCalc.c" before building this module in order to suit your per sonal 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,$day));"".
(See the section "RECIPES" near the end of this document for an example on how to print dates in any format you like.)
� "$string = English_Ordinal($number);": This function returns a string containing the (english)
abbreviation of the ordinal number for the given (cardi
nal) number "$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.
� "$string = Calendar($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 fur ther 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 "$orthodox" is given and true, the calendar starts on Sunday instead of Mon day.
� "$string = Month_to_Text($month);": This function returns the name of the given month in the
currently selected language (see further below for
details about the multi-language support of this pack
age).; If the given month lies outside of the valid range from
"1" to "12", a fatal "month out of range" error will
occur.
� "$string = Day_of_Week_to_Text($dow);": This function returns the name of the given day of week
in the currently selected language (see further below
for details about the multi-language support of this
package).; If the given day of week lies outside of the valid range
from "1" to "7", a fatal "day of week out of range"
error will occur.
� "$string = Day_of_Week_Abbreviation($dow);": This function returns the special abbreviation of the
name of the given day of week, IF such special abbrevia
tions have been defined for the currently selected lan
guage (see further below for details about the multilanguage support of this package).; (In the original distribution of this package, this is
only true for Portuguese.); If not, the first three letters of the name of the day
of week in the currently selected language are returned
instead.; If the given day of week lies outside of the valid range
from "1" to "7", a fatal "day of week out of range"
error will occur.; Currently, this table of special abbreviations is only
used by the functions ""Date_to_Text()"" and ""Calen
dar()"", internally.
� "$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 eleven
languages:

1 ==> English (de

fault)
2 ==> Fran�ais (French)
3 ==> Deutsch (German)
4 ==> Espa�ol (Spanish)
5 ==> Portugu�s (Portuguese)
6 ==> Nederlands (Dutch)
7 ==> Italiano (Italian)
8 ==> Norsk (Norwegian)
9 ==> Svenska (Swedish); 10 ==> Dansk (Danish)
11 ==> suomi (Finnish)
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()"" fur ther below to determine how many languages are actually available in a given installation of this package.
� "$lang = Language();"
� "Language($lang);"
� "$oldlang = Language($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 eleven
languages:

1 ==> English (de

fault)
2 ==> Fran�ais (French)
3 ==> Deutsch (German)
4 ==> Espa�ol (Spanish)
5 ==> Portugu�s (Portuguese)
6 ==> Nederlands (Dutch)
7 ==> Italiano (Italian)
8 ==> Norsk (Norwegian)
9 ==> Svenska (Swedish); 10 ==> Dansk (Danish)
11 ==> suomi (Finnish)
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()"" fur ther 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 sys
tems, 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: $old_language = Language_to_Text(Lan; guage("Name_of_new_Language"));
to determine the (previously) selected language.
If the so chosen language is not available in the cur rent installation, this will result in an appropriate error message, instead of silently using the wrong (a random) language (which just happens to have the same internal number in the other installation).
Note that in the current implementation of this package,
the selected language is a global setting valid for ALL
functions that use the names of months, days of week or
languages internally, valid for ALL PROCESSES using the same copy of the "Date::Calc" shared library in memory!
This may have surprising side-effects in a multi-user environment, and even more so when Perl will be capable of multi-threading in some future release.
� "$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
eleven built-in languages, therefore the value returned
by this function will be "11" if no other languages have
been added to your particular installation.
� "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 expres
sions) 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 differ
ence by looking at the code? Or by experimenting? Hint:
Try the string "a3b1c64d" with both functions.)
� "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 expres
sions) 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.)
� "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 )
{
($year,$month,$day) = Parse_Date($_);
...

}
...

}; The function returns an empty list if it can't extract a
valid date from the input string.
� "$lower = ISO_LC($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.
� "$upper = ISO_UC($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.
� "$string = Date::Calc::Version();": This function returns a string with the (numeric) ver
sion number of the C library ("DateCalc.c") at the core
of this package (which is also (automatically) the ver
sion number of the "Calc.xs" file).; Note that under all normal circumstances, this version
number should be identical with the one found in the
Perl variable "$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 ver
sion 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 cer: tain 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 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 18.0;

}
else
{

print "Sorry - you aren't 18 yet!0;

}; 4) 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;
5) 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);
$n = int( Delta_Days(: Nth_Week; day_of_Month_Year($year,$month,$dow,1),
$year,$month,$day)
/ 7) + 1;
printf("%s is the %s %s in %s %d.0,: Date_to_Text_Long($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 Octo; ber 2000.
6) 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);
7) 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);
8) 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),; "0;
print "Last $dow was: ", Date_to_Text(@prev),
"0; print "Next $dow will be: ", Date_to_Text(@next),
"0;
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
9) 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 "@hol
iday", which contains all holidays, as follows:
""$holiday[$year][$month][$day] = 1;"".

(See the description of the function ""Easter_Sun
day()"" 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; }

}

10) 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) = ($datetime =~ /^(+).()()()$/);

($year,$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:%02d0,

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 guar
antee 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 stan
dard". MS chose to keep the bug in order to be compat
ible with Lotus 123. But they have not mentioned any
thing about it in the help files.

11) 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!
}
12) How can I print a date in a different format than pro: vided 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,$day) = Today();
For example with leading zeros for the day: "Fri 03-Jan-1964": printf("%.3s %02d-%.3s-%d0,
Day_of_Week_to_Text(Day_of_Week($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);
(See also "printf" in perlfunc(1) and/or "sprintf" in perlfunc(1)!)
13) 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/%02d0, @date);; }
Note that the loop can be improved; see also the recipe below.
14) 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}), "0;

}; 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 cre
ate this array.
15) 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.

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 select
ing the language for ALL OTHER threads as well).

VERSION

This man page documents "Date::Calc" version 5.0.

AUTHOR

Steffen Beyer
mailto:sb@engelschall.com
http://www.engelschall.com/u/sb/download/

COPYRIGHT

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 addi
tionally 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.

docs.sk

comprehensive documentation repository

In section

See also