Date::Manip::Delta - Methods for working with deltas


   use Date::Manip::Delta;
   $date = new Date::Manip::Delta;


This module contains functions useful in parsing and manipulating deltas. As used in this module, a delta refers only to the amount of time elapsed. It includes no information about a starting or ending time.

There are several concepts involved in understanding the properties of a delta.


A delta consists of 7 fields: years, months, weeks, days, hours, minutes, and seconds, usually expressed as a colon-separated string. For example:


refers to an elapsed amount of time 1 year, 2 months, 3 weeks, 4 days, 5 hours, 6 minutes, and 7 seconds long.


A delta can be normalized or not. A normalized delta has values which have been made consistent with the type of data they represent. For example, a delta of:


is not normalized since 70 seconds is better expressed as 1 minute 10 seconds. The normalized form of this delta would be:


Deltas are automatically converted to a normalized form in almost all functions.

sets of fields

When normalizing a delta, fields are grouped together in sets where the exact relationship is known between all fields in the set.

For example, in a normal delta, it is known that there are exactly 60 seconds in a minute, exactly 60 minutes in an hour, etc.

It is NOT known how many weeks are in a month however. So, the year and month fields form one set, and the weeks, days, hours, minutes, and seconds form a second set.

When normalizing a delta, no data from one set will ever be mixed with data from another set.

As a result, the following delta is normalized:


Although 8 weeks is clearly more than 1 month, we don't know the relationship between the two, so they don't mix.

exact deltas

An exact delta is one which does not include any fields which cannot be exactly written in terms of seconds. For example, a delta which includes a year or month field can never be exact since there is no exact length for either.

So, the delta:


is not exact, but the delta:


is exact.

business delta

Deltas can refer to changes in either the full calendar, or they can refer to a business calendar.

Business deltas have the added complexity that there is no definite relationship between the number of work days in a work week (there may be a holiday during the week). As a result, there are three sets of fields: year/month, week, day/hour/minute/second. An exact business delta will not have a year, month, or week field.

There IS a definite relationship between hours and days, but it is probably not 24 hours = 1 day. Common definitions of a work day include 8 hours long (09:00-17:00) or 9 hours long (08:00-17:00), and any other definition may be included may be defined as long as the start time is earlier in the day than the end time. The config variables WorkDayBeg, WorkDayEnd, and WorkDay24Hr can be used to defined the length of the work day.


Each set of fields has a sign associated with it. For example, the delta "1 year ago" is written as:


Since there is no mixing of data between sets of fields, you can end up with a delta with two (or three in the case of business deltas) signs. So, the following is a fully normalized business delta:


Note that for a fully normalized delta, the leading field in each set of fields will always have a sign, even when it is redundant or unnecessary.

For example:


In a normalized delta, all fields in a set will have the same sign.



Please refer to the Date::Manip::Obj documentation for these methods.

   $err = $delta->parse($string [,$business]);

This takes a string and parses it to see if it is a valid delta. If it is, an error code of 0 is returned and $delta now contains the value of the delta. Otherwise, an error code of 1 is returned.

A valid delta is in one of two forms: colon or expanded.

The colon format is:


In the colon format, from 1 to 7 of the fields may be given. For example +D:+H:+MN:+S may be given to specify only four of the fields. No spaces may be present in the colon format. It is allowed to omit some of the fields. For example 5::3:30 is valid. In this case, missing fields default to the value 0.

The expanded format is:

   +Yy +Mm +Ww +Dd +Hh +MNmn +Ss
         +4 hours +3mn -2second
         + 4 hr 3 minutes -2
         4 hour + 3 min -2 s
         4 hr 2 s       (note that minutes are omitted)

A field in the expanded format (+Yy) is a sign, a number, and a string specifying the type of field. The sign is "+", "-", or absent (defaults to the next larger element). The valid strings (in English) specifying the field type are:

   y:  y, yr, year, years
   m:  m, mon, month, months
   w:  w, wk, ws, wks, week, weeks
   d:  d, day, days
   h:  h, hr, hour, hours
   mn: mn, min, minute, minutes
   s:  s, sec, second, seconds

Other languages have similar abbreviations.

Also, the "seconds" string may be omitted. The sign, number, and string may all be separated from each other by any number of whitespace. The string specifying the unit must be separated from a following number by whitespace or a comma, so the following example will NOT work:


At minimum, it must be expressed as:

   4hours 3minutes
   4 hours, 3 minutes

In the the expanded format, all fields must be given in the order: Y M W D H MN S. Any number of them may be omitted provided the rest remain in the correct order.

Most languages also allow a word to specify whether the delta is an amount of time after or before a fixed point. In English, the word "in" refers to a time after a fixed point, and "ago" refers to a point before a fixed point. So, the following deltas are equivalent:

  in 1 year

and the following are equivalent

  1 year ago

The word "in" is completely ignored. The word "ago" has the affect of reversing all signs that appear in front of the components of the delta. In other words, the following two strings are identical:

   -12 yr  6 mon ago
   +12 yr +6 mon

(don't forget that there is an implied minus sign in front of the 6 in the first string because when no sign is explicitly given, it carries the previously entered sign).

The in/ago words only apply to the expanded format, so the following is invalid:

   1:0:0 ago

A delta may be business mode, or non-business mode. By default, a delta is treated as a non-business mode delta, but this can be changed in two different ways.

The first way to make a delta be business mode is to pass in the 2nd argument to the function that is non-zero. If this is done, the delta will be a business delta by default.

The second way to specify whether a delta is business or non-business is to include a key word in the string that is parsed. When this is done, these strings override any value of the $business argument.

Most languages include a word like "business" which can be used to specify that the resulting delta is a business mode delta or a non-business delta. Other languages have equivalent words. The placement of the word is not important. Also, the "business" word can be included with both types of deltas, so the following are valid and equivalent:

   in 4 hours business
   4:0:0 business
   business 0:0:0:0:4:0:0

There are also words "exact" or "approximate" which serve to force the delta to be non-business mode. For backward compatibility, both are available and serve the same purpose (they no longer determine whether the delta is exact or not... that is determined only by the fields that are included as described above).

   $err = $delta->set($field,$val);

This explicitly sets one or more fields in a delta.

$field can be any of the following:

   $field   $val

   delta    [Y,M,W,D,H,MN,S]  sets the entire delta
   business [Y,M,W,D,H,MN,S]  sets the entire delta
   normal   [Y,M,W,D,H,MN,S]  sets the entire delta
   y        YEAR              sets one field
   M        MONTH
   w        WEEK
   d        DAY
   h        HOUR
   m        MINUTE
   s        SECOND

   mode     business, normal

An error is returned if an invalid value is passed in.

When setting the entire delta with "business" or "normal", it flags the delta as a business or non-business delta respectively. When setting the entire delta with "delta", the flag is left unchanged.

   $out = $delta->printf($in);
   @out = $delta->printf(@in);

This takes a string or list of strings which may contain any number of special formatting directives. These directives are replaced with information contained in the delta. Everything else in the string is returned unmodified.

A directive always begins with '%'. They are described in the section below in the section PRINTF DIRECTIVES.

   $date2  = $delta->calc($date1 [,$subtract]);
   $delta3 = $delta1->calc($delta2 [,$subtract]);

Please refer to the Date::Manip::Calc documentation for details.

   $flag = $delta->type($op);

This tests to see if a delta is of a certain type. $op can be;

   business  : returns 1 if it is a business delta
   exact     : returns 1 if it is exact
   $val = $delta->value();
   @val = $delta->value();

This returns the value of the delta. In scalar context, it returns the printable string (equivalent to the printf directive '%Dt'). In list context, it returns a list of fields.

undef is returned if there is no valid delta stored in $delta.


The following printf directives are replaced with information from the delta. Directives may be replaced by the values of a single field in the delta (i.e. the hours or weeks field), the value of several fields expressed in terms of one of them (i.e. the number of years and months expressed in terms of months), or the directive may format either the entire delta, or portions of it.

Simple directives

These are directives which print simple characters. Currently, the only one is:

   %%    Replaced by a single '%'

As an example:

  $delta->printf('|A %% B|');
     => |A % B|
Directives to print out a single field

The following directive is used to print out the value of a single field. Spaces are included here for clarity, but are not in the actual directive.

   % [+] [pad] [width] Xv

Here, X is one of (y,M,w,d,h,m,s). The directive will print out the value for that field (in the normalized delta).

If a '+' is included immediately after the '%', a sign will always be included. By default, only negative values will include a sign.

'width' is any positive integer (without a sign). If 'width' is included, it sets the length of the output string (unless the string is already longer than that, in which case the 'width' is ignored).

If 'pad' is included, it may be the character '<', '>', or '0'. It will be ignored unless 'width' is included. If the formatted delta field is shorter than 'width', it will be padded with spaces on the left (if 'pad' is '<'), or right (if 'pad' is '>'), or it will be padded on the left (after any sign) with zeroes (if 'pad' is '0').

In the following examples, $delta contains the delta: 1:2:3:4:5:6:7

   $delta->printf('|Month: %Mv|');
      => |Month: 2|

   $delta->printf('|Day: %+05dv|');
      => |Day: +0004|

   $delta->printf('|Day: %+<5dv|');
      => |Day:    +4|

   $delta->printf('|Day: %>5sv|');
      => |Day: 7    |
Directives to print out several fields in terms of one of them

The following directive is used to print out the value of several different fields, expressed in terms of a single field.

   % [+] [pad] [width] [.precision] XYZ

Here, X, Y, and Z are each one of (y,M,w,d,h,m,s). The directive will print out the value for fields Y through Z expressed in terms of field X.

Y must come before Z in the sequence (y,M,w,d,h,m,s) or it can be the same as Z.

So, to print the day and hour fields in terms of seconds, use the directive:


Any time all of X, Y, and Z are from a single set of fields, exact relationships are used.

If the X, Y, and Z fields do not all belong to the same set of fields, approximate relationships are used.

For non-business deltas, an approximate relationship is needed to link the Y/M part of the delta to the W/D/H/Mn/S part. The relationship used is that a year is assigned a length of 365.2425 days.

For business deltas, the relationship between weeks and days is set to be the length of the business week (as defined using the WorkWeekBeg and WorkWeekEnd config variables). Also, a factor of X/7 * 365.2425 (where X is the number of days in a work week) is used to determine the number of work days in a year.

If 'precision' is included, it is the number of decimal places to print. If it is not included, but 'width' is included, precision will be set automatically to display the maximum number of decimal places given 'width'.

If 'pad' is included, it may be the character '<', '>', or '0', and is used in the same way as printing out a single field.

In the following examples, $delta contains the delta: 1:2:3:4:5:6:7

      => |14.6900|
      1 year, 2 months, 3 weeks is approximately
      14.6900 months
Directives to print out portions of the delta

The following directives may be used to print out some or all of a delta.

   % [+] [pad] [width] Dt
   % [+] [pad] [width] DXY

The first directive will print out the entire delta.

The second will print out the delta from the X to Y fields inclusive (where X and Y are each one of (y,M,w,d,h,m,s) and X must come before Y in the sequence).

'pad' is optional and can be either '<' or '>' meaning to pad on the left or right with spaces. It defaults to '<'.

If a '+' is included immediately following the '%', every field will have a sign attached. Otherwise, only the leftmost field in each set of fields will include a sign.

       => |+1:2:+3:+4:5:6:7|

       => |+1:+2:+3:+4|


None known.


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


Date::Manip - main module documentation


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


Sullivan Beck (