1. Have your script find the day of the week today
2. If it's a Wed or Fri, query your db and find all projects due today+14 days into the future or sooner. Else, end the script
3. Foreach of those, see if there is another Wed or Fri between now and the due date. If so, send a reminder. If not, send a reminder and a notice to management.

If you haven't already, look at The Many Dates and Times of Perl.

I would get the epoch time, then find the day of the week with Date::Day. Adding 14*24*60*60 to the current epoch time give you the epoch time two weeks from now (since epoch is in seconds, convert 14 days to hours then minutes then seconds to find that, thus 14*24*60*60). I assume you're using a databse to store projects, so just query for all projects due BETWEEN those two dates, after having converted them into a format the db likes.

Your link is broken. Try The Many Dates and Times of Perl. Your suggestion to read this article is spot on. It is definitely worth reading.

You've got to be careful doing epoch calculations. What happens over daylight savings time shifts? You can have a 23 or 25 hour day. Depending on the time you run your script you can wind up with the wrong date. There are other opportunities for errors as well.

In most cases, you are better off using a library like DateTime (my personal favorite) to handle these calculations. Other options are mentioned in the article you suggested.

To get a date two weeks from now with DateTime simply write:

my $due_date = DateTime->now->add( weeks => 2 );
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That seems easier to understand than adding 2*7*24*60*60. It also is less likely to generate an error.


TGI says moo

Isn't this as simple as running the script every Wed and Fri (say as a cron job), and sending an email for every due date that's [0..14] (or [1..14]*) days away from today?

For the last reminder,
On Wednesdays, check if the due date is [1..2] (or [0..1]**) days away from today.
On Fridays, check if the due date is [1..5] (or [0..4]**) days away from today.

* — If you don't want notifications on the due date.
** — If you want the special notification be to sent before the due date.

Update: Untested code:

use Date::Calc qw( Day_of_Week Delta_Days Today );
use List::Util qw( min );

my ($ty,$tm,$td) = Today();

for (...{ tasks }...) {
   my ($dy,$dm,$dd) = ...{ due date of task }...;

   my $delta = Delta_Days($ty,$tm,$td, $dy,$dm,$dd);
   next if $delta < 0;   # Don't care about past-due tasks.
   next if $delta > 14;  # Don't care about due dates that far ahead.

   my $ddow = Day_of_Week($dy,$dm,$dd);

   # $cc_super is true if this is the last
   # Wednesday or Friday before the due date.
   my $days_to_wed = (3 - $ddow) % 7;
   my $days_to_fri = (5 - $ddow) % 7;
   my $days_to_next = min $days_to_wed, $days_to_fri;
   my $cc_super = ( $delta > 0 && $delta <= $days_to_next );

   send_reminder($cc_super, ...);
}
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Update: Fixed typo in code resulting in the error mentioned in reply.

hi ikegami,

the code for finding the last wednesday or friday does not work for the following scenario


due_date = Dec 15 2008 (Monday)
Today_date = Dec 12 2008 (Friday)

$delta = 3
$days_to_wed = 2, $days_to_fri = 4

$days_to_next = 2

$delta > 0 but $delta is not <= $days_to_next.
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Not using use strict; and use warnings; is bad enough. Asking why code doesn't work without turning them on and fixing the errors is even worse. It would have immediately pointed out why $days_to_wed and $days_to_fri contain the wrong values.

"Miscellaneous other allowed formats are: which dofw in mmm in YY "first Sunday in June 1996 at 14:00" ** dofw week num YY "Sunday week 22 1995" ** which dofw YY "22nd Sunday at noon" ** dofw which week YY "Sunday 22nd week in 1996" ** next/last dofw "next Friday at noon" next/last week/month "next month" in num days/weeks/months "in 3 weeks at 12:00" num days/weeks/months later "3 weeks later" num days/weeks/months ago "3 weeks ago" dofw in num week "Friday in 2 weeks" in num weeks dofw "in 2 weeks on Friday" dofw num week ago "Friday 2 weeks ago" num week ago dofw "2 weeks ago Friday" last day in mmm in YY "last day of October" dofw "Friday" (Friday of current week) Nth "12th", "1st" (day of current month) epoch SECS seconds since the epoch (negative values are supported)."