my ($timestamp, $files) = ~0;
for (<*>) {
  my $mtime = (stat)[9];   ## for atime, use (stat)[8]
  if ($mtime < $timestamp) {
    $timestamp = $mtime;
    $files = [ $_ ];
  } elsif ($mtime == $timestamp) {
    push @{$files}, $_;
  }
}
print "oldest: ", (join ',', @{$files}), "\n";