my $mgt_address = '';
my $dhcp_pool = '';
my $dhcp_network = '';
my $dhcp_mask = '';
my $dhcp_dgw = '';
my $wism_slot = '';
my $service_vlan = '';
my $native_vlan = '';
my $slot_list = '';
my @slots;
my $current_host = '';
my @ip_hosts;
my $vlan_list = '';
my %vlans;
my @network;
my $apply_status = '';
my $i;
my $status;
my $MYFILE;
my $quit = 'n';
my $vlan_number;
my $vlan_name;
my @pieces;
my @vlan_numbers;
my @vlan_names;
my @different;
our $config_string;
[download]

Instant code smell at this point. I don't even want to look further.

I see a number of variables that looks like they should have been a hash, for example. I also see variables needlessly initialized, out of some ritualistic cargo-cult behavior hoping to scare away warnings by simply working around them.