#!/usr/bin/perl

use strict;
use warnings;

use XML::LibXML;

my $parser = XML::LibXML->new();

# this call should probably be wrapped in an eval (or Try::Tiny) or at least
# tested for a valid object being returned.
my $doc    = $parser->parse_file('student.xml');

my $query  = '//student';

for my $ele ($doc->findnodes($query)){
    my $attr_text=$ele->getAttribute('id');
    if($attr_text eq '1001'){
        my $new_ele=$doc->createElement('student');
        $new_ele->setAttribute('id','1003');
        $ele->insertAfter($new_ele,undef);

        last;
    }
}

# if you can't open the file you want to know why
open(TESTFILE,">result.xml") or die "Can not open output: $!";
print TESTFILE $doc->toString;
close(TESTFILE);

exit;

__END__