Turns out flip-flops maintain their state even across subroutine calls

Not if closures are involved:

sub mk_flipflop {
 my ($start, $end) = @_;
 return sub { /$start/../$end/ }
}

for my $fh (@fhs) {
  my $ff = mk_flipflop(qr/^PP_START$/, qr/^PP_END$/);

  while (<$fh>) {
    $ff->() or next;

    # process line
  }
}
[download]