#!/usr/bin/perl
use strict;
use warnings;

my $file=shift(@ARGV) // '/etc/fstab';

my @date=reverse((localtime(( stat $file )[9] ))[0..5]);
$date[0]+=1900;
$date[1]+=1;
my $timestr=sprintf('%04u-%02u-%02u_%02u:%02u:%02u',@date);

print "$timestr\n";