#use CGI or whatever;
if( $param{in} eq 'Format HDD' ){
  #process form submission
  #redirect elsewhere or print status screen
}
else{
  #print form
}

##</code><code>##

-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=3333">st</A>)/'\$1/mg"