filemtime

filemtime is a PHP function that returns the Unix timestamp indicating the last modification time of a file or directory. It is part of PHP’s standard library and relies on the system's file metadata to report when the file’s content was last changed.

Syntax and return value

- int|false filemtime(string $filename)

- Returns the integer Unix timestamp of the last modification time on success, or false on failure. A false value typically indicates that the file does not exist or is not accessible, and a warning may be produced depending on the environment’s error reporting settings.

Behavior and notes

- The function follows symbolic links, meaning the timestamp corresponds to the target file’s modification time. If the intention is to obtain the modification time of the symlink itself, functions like lstat should be used.

- The timestamp is suitable for time-based logic, such as cache invalidation or monitoring changes to a file. It does not provide a human-readable date by itself; it is commonly formatted with date() or similar functions.

- The filename parameter can be a path to a local file or a stream-wrapped resource that PHP can stat, but behavior with remote URLs depends on the PHP configuration and the specific wrapper.

Examples

- echo date("Y-m-d H:i:s", filemtime("path/to/file.txt"));

- if (filemtime("path/to/file.txt") > time() - 3600) { /* recent change within last hour */ }

Related functions

- filemtime is often used alongside file_exists, fileatime (access time), and filectime (inode change time) to build file-aware logic.

This function is commonly employed for cache management, auto-rebuild triggers, and scripts that react to file updates.