1 function day_step(old_day,step) 
 2    local y,m,d
 3    if("0" ~= string.sub(old_day,6,6)) then
 4       m=string.sub(old_day,6,7)
 5    else
 6       m=string.sub(old_day,7,7)
 7    end
 8 
 9    if("0" ~= string.sub(old_day,9,9)) then
10       d=string.sub(old_day,9,10)
11    else
12       d=string.sub(old_day,10,10)
13    end
14 
15    y=string.sub(old_day,0,4)
16    
17    local old_time=os.time{year=y,month=m,day=d}
18    local new_time=old_time+86400*step
19 
20    local new_day=os.date("*t",new_time)
21    local res=""
22 
23    if(tonumber(new_day.day)<10 and tonumber(new_day.month)<10)then
24       res=new_day.year.."-".."0"..new_day.month.."-".."0"..new_day.day
25    elseif tonumber(new_day.month)<10 then
26       res=new_day.year.."-".."0"..new_day.month.."-"..new_day.day
27    
28    elseif tonumber(new_day.day)<10 then
29       res=new_day.year.."-"..new_day.month.."-".."0"..new_day.day
30    else
31       res=new_day.year.."-"..new_day.month.."-"..new_day.day
32    end
33    return res
34 end