Loop through an array ignores \n

$line eq "{" || "[" is interpreted as

(($line eq '{') or '[')

(as Deparse would show you). Use

$line eq '{' || $line eq '['

Moreover, $data is a scalar variable, i.e. it contains a single value. Iterating over it makes just a single step.

Normally, you'd iterate over an array:

foreach my $line (@lines)

or maybe an array reference:

foreach my $line (@$data)

or whatever else

foreach my $line ($line1, $line2, @rest_of_lines)
# or
foreach my $line (split /\n/, $message)

Using the YAML module, you can get a quick human readable format. I'm sure there are other and/or better ways to format your text, but this is one example. The benefit here is that you can transform a JSON data structure (using JSON::PP, a core Perl module that comes pre-installed) into a Perl data structure and then into a YAML structure that you can print easily. I did this with a few lines of code and a few modules, using some sample JSON data.

use strict;
use warnings;
use JSON::PP;
use YAML;

my $text = do { local $/; <DATA> };
my $json = decode_json($text);
print Dump $json;

__DATA__
{
    "ITEM":[
        {
            "-itemID": "1000000" ,
            "-itemName": "DisneyJuniorLA" ,
            "-thumbUrl": "" ,
            "-packageID": "1" ,
            "-itemPrice": "0" ,
            "-isLock": "true"
        },
        {
            "-itemID": "1000001" ,
            "-itemName": "31 minutos" ,
            "-thumbUrl": "" ,
            "-packageID": "1" ,
            "-itemPrice": "0" ,
            "-isLock": "true"
        },
        {
            "-itemID": "1000002" ,
            "-itemName": "Plaza SÚsamo" ,
            "-thumbUrl": "" ,
            "-packageID": "1" ,
            "-itemPrice": "0" ,
            "-isLock": "true"
        }
    ]
}

Output:

---
ITEM:
  - -isLock: true
    -itemID: 1000000
    -itemName: DisneyJuniorLA
    -itemPrice: 0
    -packageID: 1
    -thumbUrl: ''
  - -isLock: true
    -itemID: 1000001
    -itemName: 31 minutos
    -itemPrice: 0
    -packageID: 1
    -thumbUrl: ''
  - -isLock: true
    -itemID: 1000002
    -itemName: Plaza S┌samo
    -itemPrice: 0
    -packageID: 1
    -thumbUrl: ''

EDIT: With the new json data, I get this output:

- active: !!perl/scalar:JSON::PP::Boolean 1
  address: xx:xx:xx:xx:xx:xx
  arp_mapping_info:
    - host_id: 1
      interface_info:
        - discovery_info: ~
          host_info:
            access_to_arp: 1
            access_to_cam: 1
            access_to_cto: 1
            access_to_interface: 1
            access_to_port: 1
            address: x.x.x.x
            arp_count: 1
            arp_mib: 2
            backup_sensor_id: 0
            cam_count: 1
            cam_mib: C
            discovery1_mib: 3
            discovery2_mib: C
            engine_id: ~
            engine_mode: dynamic
            host_group_info:
              id: 0
              name: ~
              remarks: ~
            id: 1
            interface_mib: D
            interval: 1
            main_sensor_id: 1
            manufacturer: ciscoSystems
            mib_options: ~
            mode: xx
            moment: 1
            name: ~
            port_count: 1
            radius_coa_flags: ~
            radius_coa_port: ~
            radius_requests_count: 0
            radius_secret: ~
            remarks: ~
            sensor_info:
              address: x.x.xx
              architecture: xxxx
              id: 1
              last_contact: xxxx
              name: xxxx
              os_name: linux
              os_version: xxxx
              queue: 0
              remarks: ~
              status: active
              version: x.x.x-x
            snmp_read_community: public
            snmp_read_version: 1
            snmp_traps_community: ~
            snmp_traps_version: 1
            snmp_write_community: private
            snmp_write_version: 2c
            status: ok
            type: xxxx
            uplink_count: 1
            vlan_count: 1
            vlan_mib: C
          id: 1
          index: 1
          link: on
          name: x
          protocols:
            - ARP
            - NDP
          remarks: ~
          sniffer_mode: ~
          speed: 1234
          status: on
      ip_info:
        address: x.x.x.x
        date_changed: 1234
        date_created: 1234
        date_last_kerberos_login: ~
        dns_name: xxxx
        id: 6
        ip_group_info:
          id: 0
          name: ~
          remarks: ~
        kerberos_user_name: ~
        remarks: ~
  cam_mapping_info: []
  date_created: 1234
  date_last_active: 1234
  date_updated: 1234
  fingerprint_hash: ~
  id: 1234
  mac_group_info:
    id: 0
    name: ~
    remarks: ~
  manufacturer: xxx
  name: ~
  remarks: ~

Asked a coworker for help and he has just writen it in 5 minutes without big thinking...

use strict;
use warnings;

my $content = #JSON#
my @arr = split //, $content;
my $length = scalar @arr;
my $tabcounter = 0;
for (my $i=0; $i < $length; $i++) {

   print $arr[$i];
   if ( $arr[$i] eq '[' || $arr[$i] eq ']' || $arr[$i] eq '{' || $arr[$i] eq '}' || $arr[$i] eq ',') {
        print "\n";
        if ( $arr[$i] eq '[' || $arr[$i] eq '{' ) {
            $tabcounter++;
        }
        if ( $arr[$i] eq '}' || $arr[$i] eq ']' ) {
            $tabcounter--;
        }
        for (my $j=0; $j < $tabcounter; $j++) {
            print "\t";
        }
   }
}

So if anyone has to read and print out of a JSON file without any modules, here is the solution.