If you run this against your XML it will filter out the relevant tags

 
#!/usr/bin/perl
use strict;
use XML::Twig;

my $input_xml = 'big.xml';

# tags to keep
my $re = qr/u_application_i|u_ci_id|sys_class_name|name|ip_address/;
my $twig = 'XML::Twig'->new( 
  twig_handlers =>  { result => \&record }, 
);
open my $fh,'>','small.xml' or die "$!";
$twig->parsefile($input_xml);

sub record {
  my ($e,$t) = @_;
  for ($t->children){
    $_->cut unless ($_->name =~ $re);
  }
  $t->flush($fh,pretty_print => 'indented');
}
[download]

Result

<result>
    <ip_address>10.10.10.10</ip_address>
    <u_application_id></u_application_id>
    <u_display_name>lnxnmsprag27</u_display_name>
    <name>lnxnmsprag27</name>
    <u_ci_id>CI10110212</u_ci_id>
    <sys_class_name>cmdb_ci_linux_server</sys_class_name>
 </result>
[download]

Shouldn't this.

$twig->parsefile($input_xml);
[download]

Be this

$twig->parsefile($fh);
[download]

I got this error.

d_from_repair></returned_from_repair><ng_assignment_flag>ready</ng_ass
+ignment_flag><sys_class_name>cmdb_ci_esx_server</sys_class_name><u_pr
+ocurement_product_number></u_procurement_product_number><attributes><
+/attributes><u_location_stamp></u_location_stamp><fault_count>0</faul
+t_count><operational_status>1</operational_status><cfg_auto_change></
+cfg_auto_change></result></response>:
File name too long at vance.pl line 39.
 at vance.pl line 39.
 at /usr/lib/perl5/site_perl/5.22/XML/Twig.pm line 2874.
    XML::Twig::_croak("Couldn't open <?xml version=\"1.0\" encoding=\"
+UTF-8\"?><response"..., 0) called at /usr/lib/perl5/site_perl/5.22/XM
+L/Twig.pm line 794
    XML::Twig::_checked_parse_result(undef, "") called at /usr/lib/per
+l5/site_perl/5.22/XML/Twig.pm line 782
    XML::Twig::parsefile(XML::Twig=HASH(0x6003eb060), "<?xml version=\
+"1.0\" encoding=\"UTF-8\"?><response><result><chec"...) called at van
+ce.pl line 39
Debugged program terminated.  Use q to quit or R to restart,
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.
  DB<1> q
[download]

In my code I had

my $input_xml = 'big.xml';, a filename. What do you have ?

If you have my $input_xml = $client->responseContent(); then use  $twig->parse($input_xml);

poj

please delete - dupl

So here is some sample code that parses this into a hash with the sample XML embedded in the script at the __DATA__ marker:

#!/usr/bin/perl
use strict;
use warnings;
use XML::Twig;
use Data::Dumper;

my $xml;
($xml = join '',<DATA>) =~ s/\n//g;

my $twig = XML::Twig->new;
$twig->xparse($xml);

my @records = $twig->root->children;

my @items;
for my $record (@records) {
    my %item = ();
    for my $tag ($record->children) {
        $item{$tag->name} = $tag->text
    }
    push @items, {%item};
}

print Data::Dumper->Dump([\@items], ['items']);

__DATA__
<response><result><checked_in></checked_in><change_request></change_re
+quest>
<po_number></po_number><u_encryption_schema></u_encryption_schema>
<correlation_id></correlation_id><cfg_auto_provider></cfg_auto_provide
+r>
<supported_by></supported_by><u_service_catalog>true</u_service_catalo
+g>
<first_discovered></first_discovered><u_oem_part_numbe></u_oem_part_nu
+mbe>
<sent_for_repair></sent_for_repair><owned_by></owned_by>
<gl_account></gl_account><u_project_id></u_project_id><managed_by></ma
+naged_by>
<asset></asset><maintenance_schedule></maintenance_schedule>
<u_chg>false</u_chg><category>Hardware</category>
<delivery_date></delivery_date><install_status>8</install_status>
<u_maintenance_window>Friday 19:00 - 08:00</u_maintenance_window>
<virtual>false</virtual><u_sub_class></u_sub_class><dns_domain></dns_d
+omain>
<u_incident>true</u_incident>
<u_parts_software_needed></u_parts_software_needed>
<change_control></change_control><checked_out></checked_out>
<u_decommission_stamp></u_decommission_stamp><purchase_date></purchase
+_date>
<order_date></order_date><u_template></u_template><skip_sync>false</sk
+ip_sync>
<lease_id></lease_id><u_sevice_options></u_sevice_options><vendor></ve
+ndor>
<sys_id>094722740a0a3c9b01928362f7df6468</sys_id>
<u_maint_contract_sla>1</u_maint_contract_sla>
<sys_created_by>1522337</sys_created_by><u_sla_support_tie></u_sla_sup
+port_tie>
<sys_domain_path>/</sys_domain_path><subcategory>Computer</subcategory
+>
<start_date></start_date><comments></comments>
<location><link>https://foobar.bozo-now.com/api/now/table/cmn_location
+/f7
eaf4e40ff13100ac2b348ce1050e35</link><value>f7eaf4e40ff13100ac2b348ce
1050e35</value></location><unverified>false</unverified>
<justification></justification><u_disposal_date></u_disposal_date>
<sys_domain><link>https://foobar.bozo-now.com/api/now/table/sys_user_g
+rou
p/global</link><value>global</value></sys_domain><sys_tags></sys_tags>
<sys_mod_count>194</sys_mod_count><cost_cc>USD</cost_cc>
<u_total_purchase_cost>5576.73</u_total_purchase_cost><monitor>false</
+monitor>
<sys_updated_on>2015-10-13 07:33:56</sys_updated_on>
<warranty_expiration>2013-05-20</warranty_expiration>
<invoice_number></invoice_number><fqdn></fqdn><cost></cost>
<u_retail_grp></u_retail_grp><u_server_type></u_server_type>
<ip_address>10.10.10.10</ip_address>
<u_manufacture_date_dummy>2013</u_manufacture_date_dummy>
<last_discovered>2015-10-13 02:10:13</last_discovered>
<model_id><link>https://foobar.bozo-now.com/api/now/table/cmdb_model/0
+b401
34cfdaf9804103f34566ba9df5a</link><value>0b40134cfdaf9804103f3
4566ba9df5a</value></model_id>
<manufacturer><link>https://foobar.bozbozo-now.com/api/now/table/core_
+company/
41be01ee0a0a3c0e59174d9f419c61de</link><value>41be01ee0a0a3c0e59174d9
f419c61de</value></manufacturer><u_inc>false</u_inc><company></company
+>
<due></due><cfg_auto_management_server></cfg_auto_management_server>
<u_proposed>false</u_proposed><u_change>true</u_change>
<u_work_notes></u_work_notes><u_store_location></u_store_location>
<asset_tag>SCO.ST.105634</asset_tag>
<discovery_source>Manual Entry</discovery_source>
<u_application_id></u_application_id><assignment_group></assignment_gr
+oup>
<can_print>false</can_print><u_problem>true</u_problem>
<department></department><u_manufacture_date>2013-07-02</u_manufacture
+_date>
<support_group><link>https://foobar.bozo-now.com/api/now/table/
sys_user_group/4436591d0a0a3c0e76d6e42af5bba6e7</link>
<value>4436591d0a0a3c0e76d6e42af5bba6e7</value></support_group>
<u_exclusion>false</u_exclusion>
<sys_created_on>2010-11-01 21:10:45</sys_created_on>
<u_display_name>lnxnmsprag27</u_display_name><u_alias></u_alias>
<cost_center></cost_center><short_description>NOMS</short_description>
<sys_updated_by>1742882</sys_updated_by>
<name>lnxnmsprag27</name><u_environment>PROD</u_environment>
<u_function></u_function><due_in></due_in>
<u_change_approver>true</u_change_approver><install_date></install_dat
+e>
<assigned></assigned><u_active_stamp></u_active_stamp>
<u_retail_group></u_retail_group><serial_number>USE020N1VV</serial_num
+ber>
<u_work_notes__asset_></u_work_notes__asset_>
<repair_contract_id></repair_contract_id><assigned_to></assigned_to>
<mac_address></mac_address><model_number></model_number>
<schedule></schedule><u_ci_id>CI10110212</u_ci_id>
<returned_from_repair></returned_from_repair>
<ng_assignment_flag>ready</ng_assignment_flag>
<sys_class_name>cmdb_ci_linux_server</sys_class_name>
<u_procurement_product_number></u_procurement_product_number>
<attributes></attributes>
<u_location_stamp>2015-06-18 14:54:20</u_location_stamp>
<fault_count>0</fault_count>
<operational_status>1</operational_status>
<cfg_auto_change></cfg_auto_change></result></response>
[download]

This puts the entries into a hash and then dumps the hash to show that parsing works. I'll elaborate further in the other subthread.