sub is_tainted {
    return ! eval { eval("#" . substr(join("", @_), 0, 0)); 1 };
}
opendir my $dot_fh, '.' or die "Can't opendir .: $!";
my ($any_file) = readdir $dot_fh;
closedir $dot_fh;
print "tainted\n" if is_tainted( $any_file );