in reply to replace at the begining
s/<?(p\s+class=)/<$1/; [download]
#!/usr/bin/perl while(<DATA>){ s/(?<!<)p\sclass=/<p class=/; print $_; } __DATA__ <p class="Hi">Hello <p class="new">How r u [download]
<p class="Hi"\>Hello <p class="new"\>How r u [download]