my $userlink = "[CPAN:File::Find]";
  # or alternatively
  my $userlink = "[RFC:2068]";

  ...

  if ($userlink =~ /^\[CPAN:(.*?)]$/) {
    $HTMLlink = "<A href=\"http://search.cpan.org/search?mode=module&query=$1\">$1</A>";
  };
  if ($userlink =~ /^\[RFC:(.*?)]$/) {
    $HTMLlink = "<A href=\"http://www.rfc-editor.org/cgi-bin/rfcsearch.pl? ... $1\">RFC $1</A>"; # I'm not sure if
    # RFCsearch will work with a link or if it wants
    # a form ...
  };