@array1 = [ "test", "test2", "test2", "test3", "test4", "test4" ];
@array2 = [ "test", "test", "test2.1", "test4.1", "test4.2", "test4.3" ];

##</code><code>##

foreach my $item (sort @array1) {
  foreach my $found (@array2) {
    if (&match_names($item,$found)) {
      print "found a match ($item = $found\n";
      push(@save, $found);
    } # end-if
  } # end-foreach
} # end-foreach

foreach my $item (sort @array2) {
  foreach my $found (@array1) {
    if (&match_names($item,$found)) {
      print "found a match ($item = $found\n";
      push(@save, $found);
    } # end-if
  } # end-foreach
} # end-foreach

sub match_names {
  # i have this part, its just a simple regex
  # BUT this must only match in "one direction": test4 matches test 4.1, but test4.1 doesnt match test4
  return 1 if ($x =~ /some_regex_on_$y/);
}

##</code><code>##

@save contains [ "test", "test2", "test4", "test4" ];