#!/usr/bin/perl

while(<DATA>){

s/p\sclass=/\<p\\sclass=/g;
print $_;
}

__DATA__
p class="Hi">
<p class="new">

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How to search for the string where (p class=) and if before the string if character '<' doesnot exists should be replaced with <. The output should be 
<p class="Hi">
<p class="new">

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In reply to replace at the begining by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
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