use strict;
use warnings;

sub search {
		my ( $data, $neg, $pos ) = @_;
		my $regp = join "|", @$pos;
#		my $regn = join "|", map { s/^-//, $_ } @$neg; # warning:  side effects outside of sub search!
		my $regn = join "|", map { /^-?(.*)/ } @$neg; # no side effects
		my @results = grep { /$regp/ && !/$regn/ } @$data;
		return \@results;
}

my $neg = ["-bo"];
my $results = search(["bobcat", "boomerang", "beer", "bat", "aaa" ], $neg, ["b"]);
print "@$results\n";
print "@$neg\n";