die("Not safe for setuid") if ${^TAINT};

open(my $fh, ">>", __FILE__)
   or die("open: $!\n");

( my $data_pos = tell(DATA) ) >= 0
   or die("tell: $!\n");

truncate($fh, $data_pos)
   or die("truncate: $!\n");

say($fh "bar")
   or die("say: $!\n");

__DATA__
foo