use strict;
use warnings;
use Template;
use Template::Stash;

my $template_string = <<'END_OF_TEMPLATE';
[% x1 = "x1_defined_in_template" -%]
Inside the processed template:
  x1 = [% x1 %]
  x2 = [% x2 %]
  x3 = [% x3 %]
END_OF_TEMPLATE

my $stash = Template::Stash->new();
my $tmpl = Template->new( STASH => $stash );

$stash->set( x1 => 'x1_defined_in_stash_set' );
$stash->set( x2 => 'x2_defined_in_stash_set' );
$stash->set( x3 => 'x3_defined_in_stash_set' );

my $t_vars = { x3 => 'x3_defined_in_process_t_vars' };

# Process and print the template
$tmpl->process( \$template_string, $t_vars )
    or die $tmpl->error();

print "Post-process, the stash vars are:\n";
print '  x1: ', $stash->get('x1'), "\n";
print '  x2: ', $stash->get('x2'), "\n";
print '  x3: ', $stash->get('x3'), "\n";
print "Note that we could check more easily via _dump:\n";
print $stash->_dump(), "\n";

##</code><code>##

Inside the processed template:
  x1 = x1_defined_in_template
  x2 = x2_defined_in_stash_set
  x3 = x3_defined_in_process_t_vars
Post-process, the stash vars are:
  x1: x1_defined_in_stash_set
  x2: x2_defined_in_stash_set
  x3: x3_defined_in_stash_set
Note that we could check more easily via _dump:
[Template::Stash] {
        x3               => x3_defined_in_stash_set
        x2               => x2_defined_in_stash_set
        global           => {
        }
        inc              => CODE(0x18503f8)
        dec              => CODE(0x1850458)
        x1               => x1_defined_in_stash_set
        _PARENT          => <undef>
    }

##</code><code>##

use strict;
use warnings;

package Template::Capturing::Stash;
{
    use base 'Template::Stash';
    our %remembering_hash;
    sub get {
        die if @_ != 2;
        my ( $self, $var_name ) = @_;
        my $var_value = $self->SUPER::get($var_name);
#print "! Get of $var_name = $var_value\n";
        $remembering_hash{$var_name} = $var_value;
        return $var_value;
    }
    sub set {
        die if @_ < 3 or @_ > 4;
        my ( $self, $var_name, $var_value, $default ) = @_;
        die "Not yet coded to handle default" if defined $default;
        my $return_value = $self->SUPER::set( $var_name, $var_value );
#print "! Set of $var_name = $var_value\n";
        $remembering_hash{$var_name} = $var_value;
        return $return_value;
    }
}

package main;
use Template;
use Template::Stash;

my $template_string = <<'END_OF_TEMPLATE';
[% x1 = "x1_defined_in_template" -%]
Inside the processed template:
  x1 = [% x1 %]
  x2 = [% x2 %]
  x3 = [% x3 %]
END_OF_TEMPLATE

my $stash = Template::Capturing::Stash->new();
my $tmpl = Template->new( STASH => $stash );

$stash->set( x1 => 'x1_defined_in_stash_set' );
$stash->set( x2 => 'x2_defined_in_stash_set' );
$stash->set( x3 => 'x3_defined_in_stash_set' );

my $t_vars = { x3 => 'x3_defined_in_process_t_vars' };
my $out;
$tmpl->process( \$template_string, $t_vars, \$out )
    or die $tmpl->error();

print $out;
#print $stash->_dump(), "\n";

use Data::Dumper; $Data::Dumper::Sortkeys=1;
print Dumper( \%Template::Capturing::Stash::remembering_hash );

##</code><code>##

Inside the processed template:
  x1 = x1_defined_in_template
  x2 = x2_defined_in_stash_set
  x3 = x3_defined_in_process_t_vars
$VAR1 = {
          'component' => '',
          'x1' => 'x1_defined_in_template',
          'x2' => 'x2_defined_in_stash_set',
          'x3' => 'x3_defined_in_process_t_vars'
        };