my $string_to_check = "yyy foo-bar doo zzz";

my $set = '[\w-]';
my $b = qr/(?<=$set)(?!$set)|(?<!$set)(?=$set)/;

for my $check ("foo-bar doo", "bar doo") {
    if ($string_to_check =~ /$b$check$b/) {
        print "$check matched\n";
    }
}