MoveableType is a Perl-based "Personal Publishing" (aka "blogging") system written by btrott and his spouse Mena. MoveableType is driven by templates. A database of postings (and other stuff) is maintained, and HTML pages are created on demand from the database by expanding data into templates. By embedding SSI directives in templates, it's possible to arrange for Perl-generated content to be included into generated pages at page fetch time. But I wanted to embed Perl-generated stuff at page generation time. So I hacked in support for a custom tag, and can now write stuff in my MT templates like

  <MTPerl>
  require "mutate.pl";
  mutate("<$MTEntryBody$>");
  </MTPerl>
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which passes the body of an entry (post) through one of my Perl routines, and embeds the result in the output page.

Adding an <MTPerl> tag ended up being really easy, requiring two modifications to MT::Template::Context.pm

At the bottom of init_default_handlers, add   $ctx->register_handler(Perl => [ \&_hdlr_perl, 1 ]); Then add the following near the end of the package:

  sub _hdlr_perl {
     my($ctx, $args) = @_;
     my $tokens = $ctx->stash('tokens');
     my $builder = $ctx->stash('builder');
     my $res = '';
     defined(my $out = $builder->build($ctx, $tokens))
         or return $ctx->error($builder->errstr);
     $res = eval $out;
     return $@ if $@;
     $res;
  }
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Voila! You've voided your MoveableType warranty, and can do incredibly evil things with embedded Perl.