#!/usr/bin/perl -w

use strict;

LINE: while ( <DATA> ) 
{
   MATCH: while ( m#<code>(.*?)</code>#gi ) 
   {
      print "$1\n" if ( $1 !~ /foo/ );
   }
}

__DATA__
This has no match at all, and is skipped.
This has foo, but is skipped with no code block.
<code>This is acceptable</code>
so is <code></code> an embedded block, and the next.
<code></code>
<code>is foo rejected</code>
<code>foo</code>
we will skip <code> with no terminator.
and, we will also skip <code> with foo, but no terminator.
foo that preceeds <code> just </code> simple text is accepted.
here is <code> another </code> example.
but <code> Perl </code> will accept foo outside the block.
The foo can be in advance, as every <code> hacker </code> knows.
Doubled matches like <code></code> foo <code></code> are evil.
This should <code> skip the second loop</code><code> foo </code>.
This <code> foo </code> should  <code> skip the first loop </code>.