Select Code to Download

my @list= qw(a b c a c);
my $w="kandabbbc";
...
   @list = grep {!/\Q$a/} @list;
}
print $w;

my %saw;
for (@list) {
    next if $saw{$_}++;
    # ...
}

my @list= qw(a b c a c);
my $re = join '|', @list;

my $re=join "", @list;
$re="[$re]";