use Template::Alloy;
use POSIX qw(tmpnam);

my $file1 = tmpnam;
my $file2 = tmpnam;
END { unlink $file1 };
END { unlink $file2 };


if (open my $fh, ">", $file1) {
    print $fh "I am file1 ($file1).
title = (<TMPL_VAR name=title>).
page  = (<TMPL_VAR name=page>).
------------------
<TMPL_PROCESS \$page>
------------------
<TMPL_GET page3.eval>
";
    close $fh;
}

if (open my $fh2, ">", $file2) {
    print $fh2 "I am file2 ($file1).
title = (<TMPL_VAR name=title>).
";
    close $fh2;
}

my $ht = Template::Alloy->new(filename => $file1, absolute => 1);
$ht->param(title => 'The title');
$ht->param(page  => $file2);
$ht->param(page3 => sub { "This is a dynamically included string.\ntitle = (<TMPL_VAR name=title>)\n"});
print $ht->output;

__END__
prints 

I am file1 (/tmp/filessyE4j).
title = (The title).
page  = (/tmp/filez6O6TO).
------------------
I am file2 (/tmp/filessyE4j).
title = (The title).

------------------
This is a dynamically included string.
title = (The title)