Thanks a lot to all. The code provided by you was working as per my requirement. I am from Java background from past 9 years, recently took up work on Perl. As I am new to Perl, I am not very familiar with RegEx.. trying to learn :) Thanks a lot for your time and help. I had tried to do using LibXML. Here is my code... Even I added sort functionality. But it is incomplete,, commented the sort part.

#!/usr/bin/perl
use strict;
use warnings;

use strict;
use XML::LibXML;

my ($inputfile,$struct,$outputfile,$parser)

indentXML();
sortOnPUI();



sub indentXML
{
$inputfile = 'OpsbankII_10_items.xml';
$parser = XML::LibXML->new();
$struct = $parser->parse_file($inputfile);
#print $struct->toString(2);
$outputfile="output.xml";
print $struct->toFile($outputfile,2);
}

sub sortOnPUI
{
my $rootel = $struct -> getDocumentElement();
my $rootelname = $rootel -> getName();
print "Root element is a $rootelname\n";

my @items = $rootel->getElementsByTagName('item');

foreach my $item (@items) {
     my @itemids = $item->getElementsByTagName('itemid');
    foreach my $itemid (@itemids){
        #print "itemid content is ",$itemid->textContent,"\n";
        my @attrs= $itemid->attributes;
        foreach my $at (@attrs) {
          #print "itemid attribute content is ",$at->textContent,"\n";
          if ($at->textContent eq "PUI") {
              print "Attribute is ", $at->textContent," and value is "
+, $itemid->to_literal," \n";
             # my @sorted_class_elems  
            #      = sort { $a->findvalue('itemid') <=> $b->findvalue(
+'itemid') }
                #    @items;
                  }#if
            }#foreach
        }#foreach
    }#foreach
}
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