: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

:desc
Retrieves the last modification date of 'file_name' as a Unix timestamp.

:see
>sys
>time

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