# Return false if either files doesn't exist, or if we
# cannot stat either file.
sub is_same {
    my ($file1, $file2) = @_;
    return unless -f $file1 && -f $file2;
    return unless my ($dev1, $ino1) = (lstat $file1)[0, 1];
    return unless my ($dev2, $ino2) = (lstat $file2)[0, 1];
    return $dev1 == $dev2 && $ino1 == $ino2;
}