sub smaller_than_30
{
    my (@result);     # 局部變量，暫時儲存返回值
    foreach $_ (@_)   # 掃描參數列
{   
       if ($_<30)     # 判斷是否符合條件
       {
          push (@result, $_);    # 將符合條件的數加入列表中
}
}
return @result;     # 傳回最后的列表
}
@number = (20..40);
@num_list = smaller_than_30(@number);
foreach $num (@num_list){
print $num,"  ";
}