How to create a file name with current date & time in lua? - lua

Question

I want to write a table into a file which named by the date and time it created.
I can open a file with hard coded name, write the table into it, like below:
FILENAME_EVENTS="Events.txt" -- filename in string
local fp=io.open(FILENAME_EVENTS, a) -- open a new file with the file name
io.output(FILENAME_EVENTS) -- redirect the io output to the file
-- write the table into the file
for i, e in ipairs(eventlist) do io.write(e.title, e.category, e.ds, e.de, e.td) end
But when I try to:
FILENAME_EVENTS=os.date().."\.txt" -- filename in string with date
local fp=io.open(FILENAME_EVENTS, a) -- open a new file with the file name
io.output(FILENAME_EVENTS) -- redirect the io output to the file
-- write the table into the file
for i, e in ipairs(eventlist) do io.write(e.title, e.category, e.ds, e.de, e.td) end
I got an error
bad argument #1 to 'output' (10/06/11 17:45:01.txt: Invalid argument)
stack traceback:
[C]: in function 'output'
Why this "10/06/11 17:45:01.txt" is an invalid argument? due to it contains spaces or '/'? Or any other reasons?
BTW, the platform is win7 Pro + Lua 5.1.4 for win

Answer 1

Apparently it's both / and : that bork. The first probably because it is regarded as directory separator. This can be demonstrated as below:
fn=os.date()..'.txt'
print(io.open(fn,'w')) -- returns invalid argument
fn=os.date():gsub(':','_')..'.txt'
print(io.open(fn,'w')) -- returns nil, no such file or directory
fn=os.date():gsub('[:/]','_')..'.txt'
print(io.open(fn,'w')) -- returns file(0x...), nil <-- Works
BTW, instead of using strange gsub and concatenation tricks, you might also consider using something like
fn=os.date('%d_%m_%y %H_%M.txt')