calculating ages

[Jean-Pierre Radley]

In article <354 at cms2.UUCP> alan at cms2.UUCP (Alan McCain) writes:
>Can anyone give me some ideas of calculating the ages of people?  I have an
>application where I am generating a report using awk and part of the report
>is figuring out the age of someone using their birth date in the form
>yymmdd.  I would like a solution in awk but am welcome to other suggestions,
>too.
>

The late Fred Buck was handed a hypothetical manual page for something that
would do date calculations. So he wrote the program to fit the manual page.
It's a bit too much to include all of it here (and it's C source, not shell
language), so I'm emailing it to you.

But here's the man page:

Name
	datecalc - date math filter

Syntax
	datecalc [-mdy] {+|-}offset [date]
	 or
	datecalc -i [-mdy] [{+|-}offset] basedate [newdate]

Description

	Datecalc performs addition or subtraction upon the date passed to it,
	and returns the calculated date to standard output. If no date is
	specified on the command line, datecalc reads standard input for a list
	of dates separated by newlines, performs the specified arithmetic on
	each date in the list, and sends the calculated date(s) to standard
	output.

	The default order for day, month and year on input is month, day, year.
	If the "-mdy" argument is given, then the order of month, day and year
	on input is taken to be whatever order the letters 'm', 'd' and 'y'
	appear in the command-line argument. So "-mdy" means "month, then day,
	then year" and is the same as the default; "-dmy" means "day, then
	month, then year" and so forth.

	The offset must be preceded by a plus or a minus sign.

	The format of date, whether on the command line or in standard input,
	is up to the user. If day, month, and/or year are not separated by any
	non-numeric characters, then each field must contain at least two
	characters ("03" instead of "3"); if delimiters are used, single-digit
	fields are permissible. If alphabetic format is used for the month,
	output will mimic input format but the month name will be no longer than
	three characters.

	If the "-i" switch is present, and if it's present it has to be the
	first command-line switch, then the whole deal is different. The "-i"
	stands for "interval", and with this switch, this program will report
	either the number of days separating two specified dates, or the latter
	of the two dates if the interval between the dates is greater than or
	less than the specified 'offset', where 'offset' can be positive or
	negative. If the "-i" switch is present, then a basedate must be
	specified on the command line. If the "newdate" isn't specified on
	the command line, then standard input is examined for a list of newdates
	to compare with the command-line basedate. The type of output when "-i"
	is present depends on whether an interval argument is also present: if
	no interval is specified, then the output consists of the number days
	separating the basedate and the new date. If an interval argument,
	preceded by a plus sign or a minus sign, is specified, then the output
	consists of the new date if the new date is outside (plus sign) or
	within (minus sign) the specified interval from the basedate.

	An easy way to remember this is that with the "-i" option, an offset of
	"+x" means "report any received dates greater than x days distant from
	the basedate"; an offset of "-x" means "report any received dates less
	than x days distant from the basedate"; and no offset at all means
	"report the number of days between the basedate and the newdate."

Examples

	datecalc -dmy +20 27-8-88	returns		16-9-88
	datecalc +20 8/27/88		returns		9/16/88
	datecalc +20 08-27/88		returns		09-16/88
	datecalc +20 August 27, 1988	returns		Sep 16, 1988

	datecalc -ydm +20tS		Scans standard input for dates in year,
					day, month format, and returns the date
					20 days after each input date, in the
					format of each input date

	datecalc -i -7 9/1/88 9/28/88	returns		nothing, because 9/28
							isn't within 7 days of
							9/1

	datecalc -i +7 9/1/88 9/28/88	returns		9/28/88

	datecalc -i 9/1/88 9/28/88	returns		27

	datecalc -i -dmy 1-Sep-88	Scans standard input for dates in day,
					month, year format, and reports for each
					input date the number of days' diff-
					erence between that date and 1-Sep-88

Notes
	Valid dates range only from 1970 through 1999.
	
Author
	Fred Buck
-- 

 Jean-Pierre Radley          HIGH-Q	     jpr at jpradley	CIS: 72160,1341