use Date::Calc qw(Today Add_Delta_YMD Days_in_Month);
my ($year, $month, undef) = Add_Delta_YMD( Today(), 0, -1, 0 );
printf "start: %04d-%02d-%02d\n", $year, $month, 1;
printf "  end: %04d-%02d-%02d\n", $year, $month, Days_in_Month($year, $month);