:sig
time_t file_mtime(String file_name)

:params
file_name : name of the file
return value : Unix time stamp of the file's last modification

:see
>sys
>time

:content
Retrieves the last modification date of `file_name` as a Unix timestamp.

## Related Concepts

- PHP: `filemtime()`
- JavaScript / Node.js: Node `fs.statSync().mtimeMs` or `fs.promises.stat()`