I created a small Perl program to convert relative dates to absolute dates in the format that I use for my calendar. My current calendar file looks like this.

2008
    08
        2008-08-12
        2008-08-13
    09
        2008-09-10
        ...

If I want to add a date and I don’t know the actual numbers, I can use the following program to convert the date. It will also respect the whitespace in front of the text.

#!/usr/bin/perl -w
use v5.10;

use strict;
use warnings;

use Date::Manip;

Date_Init('Language=Dutch');

my $inp = <>;

if (my ($ws, $date) = $inp =~ m/^(\s*)(.+)$/) {
    say $ws . UnixDate($date, "%Y-%m-%d");
}
else {
    print $inp;
}

I use Date::Manip for parsing the date. It works with human language style dates like thursday. I added Date_Init so it will parse Dutch days like donderdag. Also I use Perl 5.10, because I can. It has some nice features.

To use it put this script in the path. I called it refdate.pl. To use it type a date and type !!refdate.pl<Enter>. In Vim this will call the program on the current line. The date will be formatted in the YYYY-MM-DD format.