my @stuff = qw/foo bar baz boing/;
my %ref = map { $_ => 1 } qw/bar boing/;

my @filtered = grep { !$ref{$_} } @stuff;

foreach $i (@a) {
    $x = 0;
    foreach $u (@b) {
        if ($u eq $i) {
            $x = 1;
            last;
        }
    }
    unless ($x) {
        print "$i\n";
    }
}

use strict;
use warnings;
use Data::Dumper;

my @stuff1 = qw/a b c d/;
my @stuff2 = qw/a d/;

my %seen;          
my @stuff1_only; 
my $element;

foreach $element(@stuff2) {
          $seen{$element} = 1;
}

foreach $element (@stuff1) {
          unless ($seen{$element}) {
                  push (@stuff1_only, $element);
          }
}

print Dumper \@stuff1_only;

my @lista=qw(a b c d e);
my @listb=qw(c p k a r p b);

my $regexp='\Q'.join('\E|\Q',@lista).'\E';
my @result=grep{!/$regexp/}@listb;

print "@result\n";