DateTime lets you specify a formatter, which is used whenever you print or stringify a DateTime object:

use strict;
use warnings;
use DateTime;
use DateTime::Format::Strptime;

my $start_of_week =
    DateTime->today()
            ->truncate( to => 'week' );
$start_of_week->set_formatter( DateTime::Format::Strptime->new(pattern
+ => "%d-%m-%y") );
    
for ( 0..6 ) {
    my $teden = $start_of_week->clone()->add( days => $_ );
    print "$teden\n";
}
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This is useful when you print in many places of your code and want the same format. Remark: installing DateTime::Format::Strptime unleashed a cascade of dependencies on my Perl install...