Most likely you can do this with the World's Simplest Templating Engine:

use File::Slurp 'read_file';
my $template = read_file($template_name);
1 
  while $template =~ s/\[%\s*INCLUDE\s(.*?)\s*%\]/read_file($1)/msge;
print $template;
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This will not handle include parameters and will not search different directories, but you can add that by replacing read_file by a subroutine more suited to your needs.

Update: Corrected regular expression according to pc88mxer's comment

A little nit... wouldn't you want (.*?) for $1?

From the syntax exmples in the docs it seems you only have to parse

[% PROCESS template var=val var=val ... %]
[% INCLUDE template var=val var=val ... %]
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Since there's no tag nesting, it can be done with regexes.

A first ad-hoc attempt, not tested:

my $re = qr{
   \[%-?        # start tag
   \s*
   (?:PROCESS|INCLUDE)
   \s+
   (\S+)        # template name
   .*?          # any parameters you're not interested in
   -?%\]        # end tag
}xs;
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Try if it matches all you need, if not refine it.

And yes, that's only an ad-hoc solution, and wo't scale very well.

(Update: template name is probably \S+, \w+ is too restrictive)

To build on this solution, to properly handle passing parameters I think you need to replace

[% INCLUDE file var1=val1 var2=val2 ... %]
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with:

[% BLOCK _inline_file %]
...contents of file...
[% END BLOCK %]

[% INCLUDE _inline_file var1=val1 var2=val2 ... %]
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and the same for PROCESS directives. There can be complications if you use INCLUDE and PROCESS with BLOCK identifiers. In that case you'll have to determine if the template argument refers to a file or a BLOCK. Finally, if you include or process a template file twice you'll want to make sure you don't define the corresponding inlined block twice.

btw, this would be an excellent question for the template toolkit list.

You might want to look at Template::Multipass actually. It could be what you are looking for, or at least a start.

You can process the template and then save the resulting page wherever you want. Either giving it default values or not. Consider:

use Template;

my $template = Template->new({
    INCLUDE_PATH => $template_path,
}) || die $!;

my %vars = ();
my $pre_processed_template = '';

# this will get you the processed template
$template->process('master_template.html', \%vars, \$pre_processed_tem
+plate);

# now you can save the processed page with the contents of $pre_proces
+sed_template.
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I assume that what you are looking for are is the compiled templates that are converted into Perl code.

The Template Toolkit documentation for COMPILE_EXT cover this.