use Date::Calc qw( Days_in_Month Add_Delta_Days Day_of_Week );

 $day = Days_in_Month($year,$month);
 while (1)
 {
     while ($holiday[$year][$month][$day])
     {
         ($year,$month,$day) =
             Add_Delta_Days($year,$month,$day, -1);
     }
     $dow = Day_of_Week($year,$month,$day);
     if ($dow > 5)
     {
         ($year,$month,$day) =
             Add_Delta_Days($year,$month,$day, 5-$dow);
     }
     else { last; }
 }