:sig
u64 file_mtime(String file_name)

:params
file_name : path to inspect, resolved against the unit's directory
return value : last-modified time as a Unix timestamp, or 0 if missing

:content
Returns a file's last-modified time as a Unix timestamp. Compare two files' mtimes for cache-freshness checks, or test for `> 0` to confirm a file exists with a real timestamp.

:example
file_put_contents("/tmp/doc-mtime.txt", "x");
print(file_mtime("/tmp/doc-mtime.txt") > 0 ? "has a modification time" : "missing", "\n");

:see
>sys
file_stat
time
