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From: [email protected] (Ariel Faigon)
Subject: Re: day of the week from date?
Message-ID: <[email protected]>
Followup-To: comp.lang.perl
Summary: Zeller congruence in perl (repost)
Keywords: day-of-week, perl
Sender: [email protected] (UseNet News account)
Reply-To: [email protected]
Organization: National Semiconductor Corp.
References: <[email protected]>
Date: Thu, 10 Jun 1993 21:11:04 GMT
Lines: 48


[email protected] (Yan K. Lau) just wrote:
: How can I figure out which day of the week it is (e.g. Wed) from a date
: (not necessarily today) in day month year format (e.g. 9 Jun 93)?  Is this easy to do?

Here is a script posted by Carl Rigley to this newsgroup (almost three years ago. Wow).
which does this efficiently.
So the answer to this question is: Yes it is easy if you've read this newsgroup
since it was established or know how to search in the archives :-)

#!/usr/local/bin/perl
# From: [email protected] (Carl Rigney)
# Summary: zeller's congruence
# Keywords: weekday perl subroutine
# Date: 2 Oct 90 17:21:14 GMT
# Organization: Advanced Micro Devices; Sunnyvale, CA
#
# Here's a simple subroutine to calculate Day of the Week using
# Zeller's Congruence, which I've found very useful.  A lot of
# the temporary variables could be omitted by making it harder to read.

# usage: zeller yyyy mm dd
unless ($#ARGV == 2) {
   print STDERR "Usage: $0 yyyy mm dd\n";
   exit 1;
}
$day = &weekday(@ARGV);
print $day,"\n";

sub weekday {
       local($year,$month,$day)=@_;
       local($y,$m,$c,$yy,$z);

       local(@wday) = ( "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" );

       $y = $year;
       $m = ($month + 10) % 12;
       $y-- if ($m > 10);
       $c = int ( $y / 100 );
       $yy = $year % 100;

       $z = ( int ( (26*$m - 2)/10) + $day + $yy + int($yy/4) + int ($c/4) - 2*
$c ) % 7;
       return $wday[$z];
}

---
Ariel Faigon    [email protected]