We check the page to see if it contains any strings. If it does not, we consider it not to have a template and add the definitions ourselves. The following is needed in catalog.cfg:

Pragma  init_page=wrap_page

Sub <<EOS
  sub wrap_page {
  my $pref = shift;
  return if $$pref =~ m{\@_[A-Z]\w+_\@};
  $$pref =~ m{<!--+ title:\s*(.*?)\s+-->} and $Scratch->{page_title} = $1;
  $$pref = <<EOF;
\@_MYTEMPLATE_TOP_\@
<!--BEGIN CONTENT -->
$$pref
<!-- END CONTENT -->
\@_MYTEMPLATE_BOTTOM_\@
EOF

  return;
  }
EOS

In this real-life example, we want to automatically attach header and footer to every served page. We also have four different templates, and want to include them depending on the path of the page being served.

Pragma  init_page=wrap_page
Sub <<EOS
sub wrap_page {
  my $pref = shift;
  my $tmpl;

  if ( $Session->{last_url} =~ m#^/www(/|$)# ) {
    $tmpl = "www"
  } elsif ( $Session->{last_url} =~ m#^/plus(/|$)# ) {
    $tmpl = "plus"
  } elsif ( $Session->{last_url} =~ m#^/hp(/|$)# ) {
    $tmpl = "hp"
  } elsif ( $Session->{last_url} =~ m#^/adm(/|$)# ) {
    $tmpl = "adm"
  }

  $Scratch->{subsite} = $tmpl || $Scratch->{subsite} || "plus";

  $$pref = "[include templates/$Scratch->{subsite}-top]" .
    $$pref .
    "[include templates/$Scratch->{subsite}-bottom]";

  return;
}
EOS

Note that we explicitly check for supported template types (www, plus, hp or adm) to minimize the chance of abuse. Invalid or unmatched templates default to the previously used template, or plus as a bottom line and the files templates/plus-top and templates/plus-bottom are included then.

You might wonder in what cases would the code fail to match the template? Well, obviously, users could simply try to access non-existent pages. The other common issue are ActionMaps such as /scan or /process.