int fileatime (string filename)
Returns the time the file was last accessed, or false in case of an error. The time is returned as a Unix timestamp.
The results of this function are cached. See clearstatcache() for more details.
Note: The atime of a file is supposed to change whenever the data blocks of a file are being read. This can be costly performancewise when an appliation regularly accesses a very large number of files or directories. Some Unix filesystems can be mounted with atime updates disabled to increase the performance of such applications; USENET news spools are a common example. On such filesystems this function will be useless.