#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
use Date::Calc qw( Today Day_of_Week );

my ($year,$month,$day) = Today();

my $week = int(($day + Day_of_Week($year,$month,1) - 2) / 7) + 1;

say "Week number: " . $week;

__END__

$ perl test.pl
Week number: 3