#!/usr/bin/perl

use strict;
use warnings;

my @a = qw(1 2 3 4 5 6);
my @b = qw(9 2 7 6 5 4);


my @are_equal = compare_arrays(\@a, \@b);

print $_,"\n" for @are_equal;

sub compare_arrays {
    my ($first, $second) = @_;
    my @tmp;
    no warnings; # silence spurious -w undef complaints
    #return 0 unless @$first == @$second;
    for (my $i = 0; $i < @$first; $i++) 
    {
        if ($first->[$i] eq $second->[$i])
        {
            push(@tmp,$first->[$i]);
        }
    }
    return @tmp;
}

C:\>arrays.pl
2
5

my @a = qw/ foo bar baz boo far rab oob /;
my @b = qw/ foo BAR baz BOO far /;

sub compare_arrays
{
  my ($first, $second) = @_;
  my @tmp;
  for my $elm (@$first) 
  {
    if(defined($elm) && grep{defined($_) && $elm eq $_}@$second)
    {
      push(@tmp,$elm);
    }
  }
  return @tmp;
}

sub compare_arrays
{
  my ($first, $second) = @_;
  my %found;
  my @tmp;
  for my $elm (@$first) 
  {
    if(defined($elm) && grep{defined($_) && $elm eq $_}@$second && !$found{$elm})
    {
      push(@tmp,$elm);
      $found{$elm}++;
    }
  }
  return @tmp;
}

sub compare_arrays
{
  my ($first, $second) = @_;
  my %found=map{($_,1)}@$first;
  my @tmp;
  for my $elm (@$second)
  {
    if(defined($elm) && $found{$elm})
    {
      push(@tmp,$elm);
    }
  }
  return @tmp;
}