the problem is that there are still 10 elements if you just undef the match(es):

my @array = 1..10;

print "@array\n";

my $item = 3;

foreach my $element (@array) {
   undef $element if ($element eq $item);
}

print "@array\n";
print $#array + 1;
[download]

see, the array doesn't actually shrink. when you do a print $#array + 1 you still get a 10 (assuming there were 10 elements to start like there were here).

to get rid of the phantom element(s), you could use splice like this:

my @array = 1..10;

print "@array\n";

my $item = 3;
my @empties;
my $count;

foreach my $element (@array) {
    if ($element eq $item) {
    undef $element;
    push @empties, $count;
    }
    $count ++;
}

foreach (@empties) {
    splice (@array, $_, 1);
}

print "@array\n";
print $#array + 1;
[download]

hth,
--au