Convert date to Unix time withoug os.time() in Lua

Question

I am developing a plugin written in Lua.

I need a way to calculate Unix time or at least a way to compare 2 date strings

The function I can use only returns date string in the following format

"1/17/2014 6:50 PM"

Is there a way to convert this string to a Unix time?

Unfortunately I don't have access to the OS library so things like os.time() does not work.

Is there a library or something similar that I can work with?

+Yeah I thought about splitting the string into parts, but I also need a way to add/subtract time

Answer 1

Just compare normalized timestamps:

function normalize(a)
    local m,d,y,h,mi,n=a:match("(%d+)/(%d+)/(%d+)%s+(%d+):(%d+)%s+(%w+)")
    if n=="PM" then h=h+12 end
    return string.format("%04d%02d%02d%02d%02d",y,m,d,h,mi)
end

Date arithmetic is another story. For a complete, pure Lua date library, see luatz or https://github.com/Tieske/date.

Answer 2

If you need to only compare two time, you don't need to get each time's Unix timestamp. One possible solution is to get the time fields from the string like this:

local time = "1/17/2014 6:50 PM"
local month, day, year, hour, minute, am_pm = time:match("(%d+)/(%d+)/(%d+)%s+(%d+):(%d+)%s+(%w+)")

print(month, day, year, hour, minute, am_pm)

Output: 1 17 2014 6 50 PM

Then compare two time from comparing their year, if they are equal, then month, and so on. Remember to use tonumber to compare them by number, not the string itself.