#!/usr/bin/perl
while($line = <DATA>){

@valid_entities= ('<a>','<abbr>','<acronym>');
my %htmlenties = map { $_ =>1 } @valid_entities;
@valid_entities= ('a','abbr','acronym','br');# remove tags
my %htmlenties = map { $_ =>1 } @valid_entities;
$line =~  s/<(\/?([^>]*?)\/?)>/exists $htmlenties{$2} ? "<$1>" : defined ($1) ? "&lt;$1&gt;" : "&lt;"/xeg;
print $line;

<helloe>How r u <a> www.google.com</a>
<hi>How r u </hi><et,-2><>