my @list1 = get_from_some_place();
my @list2 = get_from_some_other_place();

--------

# Hash method

my %lookup_hash;
@lookup_hash{@list2} = undef; # This is a hashslice. We don't care about the values.

unless (exists $lookup_hash{$list1[0]})
{
    # Do something here
}

--------

# grep method

unless (grep { $_ eq $list1[0] } @list2)
{
    # Do something here
}