PHP Manual: filemtime
filemtime
Description
int filemtime ( string filename )This function returns the time when the data blocks of a file were being written to, that is, the time when the content of the file was changed.
Return Values
Returns the time the file was last modified, or FALSE in case of an error. The time is returned as a Unix timestamp, which is suitable for the date() function.
Notes
Note: The results of this function are cached. See clearstatcache() for more details.
Tip: As of PHP 5.0.0 this function can also be used with some URL wrappers. Refer to Appendix O for a listing of which wrappers support stat() family of functionality.