Update

I tested the change above, and found that it does not correct the problem, you need to use the form I have below with undef as the second arg to insertAfter. It is possible that this is a result of different versions, so test for yourself.

End update

I was just going to post the same thing as above after a quick test script. Here is the output produced by making the change:

<?xml version="1.0" encoding="utf-8"?>
<University>
    <students>
        <student id="1000"/>
        <student id="1001"><student id="1003"/></student>
        <student id="1002"/>
    </students>
</University>
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On a different note, you should always have use strict; and use warnings; as well as check for critical failures in your code, like this:

#!/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__
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