while(<FILE>) {
   push @stock,$_;
}

# Would be better as...
@stock = <FILE>;

##</code><code>##

while(@stock) {
 foreach $line (@stock) {

##</code><code>##

while (my $line = <FILE>) {
    # do stuff
}

##</code><code>##

open $item[2], ">>some_filename";
       put_items_into_it;
    close $item[2]

##</code><code>##

my $cat = undef;
while (my $line = <FILE>) {
    @items = split('|', $line);
    if ($cat ne $items[2]) {
        close OUTFILE if (defined $cat);
        open OUTFILE, ">>some_filename";
        $cat = $items[2];
    } 
    print OUTFILE ## Whatever ###;
}
close OUTFILE;

##</code><code>##

delete_that_line_from_stock;