Subtract days from today date and compare after - perl

Question

Following situation.
I have a file named 2018_12_03_FileName.log. Now I get the date from the file (2018_12_03).
I want to convert the string to a DateTime object, which works too.
$chars =~s/_//g;
$chars = Time::Piece->strptime("$chars", "%Y%m%d");
$chars = $chars->strftime("%d/%m/%Y");
Output
03/12/2018
After that I want to get the date today - 14 days. But here is one of my two problems. I tried many things, but couldn't find any real solution working for me.
my $day14 = DateTime->now();
$day14 -= (2 * ONE_WEEK);
Error:
Cannot subtract 1209600 from a DateTime object (DateTime=HASH(0x6f2d84)). Only a DateTime::Duration or DateTime object can be subtracted from a DateTime object.
Now the second problem is, I want to compare these two dates and look if the file date is in range or not.
my $cmp = DateTime->compare($chars, $day14);
Error:
Argument "15/07/2019" isn't numeric in numeric eq (==) at
A DateTime object can only be compared to another DateTime object (03/12/2018, 15/07/2019).
So how can I subtract 14 days from the today date and how can I compare these two dates after?

Answer 1

You're slightly muddling up two Date/Time ecosystems that don't work well together.
You can do this using Time::Piece and Time::Seconds.
use feature 'say';
use Time::Piece;
use Time::Seconds;
my $chars = '2018_12_03';
my $tp = Time::Piece->strptime($chars, '%Y_%m_%d');
my $date14 = $tp - (2 * ONE_WEEK);
say $tp->strftime('%d/%m/%Y');
say $date14->strftime('%d/%m/%Y');
Output:
03/12/2018
19/11/2018
Or you can do it using DateTime and friends.
use feature 'say';
use DateTime;
use DateTime::Format::Strptime;
my $date_parser = DateTime::Format::Strptime->new(
pattern => '%Y_%m_%d',
on_error => 'croak',
);
my $chars = '2018_12_03';
my $dt = $date_parser->parse_datetime($chars);
my $date14 = $dt->clone->subtract( weeks => 2 );
say $dt->strftime('%d/%m/%Y');
say $date14->strftime('%d/%m/%Y');
Output:
03/12/2018
19/11/2018
As for your last question, you can compare either Time::Piece objects or DateTime objects using the standard Perl comparison operators (<, ==, >=, etc). But you have to compare two objects of the same type.

Answer 2

Just another option, Time::Moment makes date math really simple:
use strict;
use warnings;
use Time::Moment;
my $chars = Time::Moment->from_object(Time::Piece->strptime("$chars", "%Y%m%d"));
my $day14 = Time::Moment->now_utc->minus_days(14)->at_midnight;
print $day14->strftime('%d/%m/%Y');
These objects can be compared with normal operators like with DateTime and Time::Piece. Just keep in mind that, since you only care about the day and not time of day, all math should be done according to the same time zone, of which the easiest is of course UTC.