But a simple template basically comes down to some text ... [% variable_name %]... some more text. If this is the case with your templates you can easily parse them directly with something like the following:

local $/;
my $text = <DATA>;

while ($text =~ /\[%(.*?)%\]/g) {
    print "$1\n";
}

__DATA__
some text ... [% variable_name %] ... some more text
[% variable_name2 %] [% variable_name3 %] ... some more text
some text ... [% variable_name4 %]
[download]

use warnings;
use strict;
use Template;

my $tt = Template->new();
my %data_href = (
                 fname => 'William',
                 lname => 'Shakespeare',
                 );

my %data_map = (
                first_name => 'fname',
                last_name => 'lname',
                );

$tt->process(
             \*DATA,
             {
                 data_href => {
                     map { $_ => $data_href{ $data_map{$_} } }
                     keys %data_map
                 },
             }
             )
    or die $tt->error(), "\n";

__END__
New third party template
========================
First name : [% data_href.first_name %]
Last name  : [% data_href.last_name %]
[download]

Here's a sneaky thought - run the template, but give it a tied hash which traps and output the key on each attempted access to a hash value. You'll still miss any hash keys which are conditionally accessed, but it should do as a good first run.

Looks like Tie::Trace might do the job nicely.

use Template;

{
    package MyStash;
    use base qw(Template::Stash);

    sub undefined {
        my $self = shift;
        my @ident = shift;

        print "(".join("|",@ident).")\n";

        if (@ident > 1) {
            return '';
        } elsif ($ident[0] eq 'adjective') {
            return 'red';
        } elsif ($ident[0] eq 'noun') {
            return 'fox';
        } elsif ($ident[0] eq 'verb') {
            return 'jumped';
        } else {
            return '';
        }
    }
}

my $stash  = MyStash->new;
my $string = "The [% adjective %] [% noun %] [% verb %] over the river
+.\n";
Template->new(STASH => $stash)->process(\$string);
[download]

And if you'd rather use CGI::Ex::Template (which is Template::Toolkit compatible template wise) you could use the following code (I'd use CGI::Ex::Template personally - but that might be because I'm intimately familiar with it :)).



use CGI::Ex::Template;

my $cet = CGI::Ex::Template->new(
    UNDEFINED_GET => sub {
        my $self = shift;
        my $ident = shift;

        print "(".join("|",@$ident).")\n";

        if (@$ident > 2) {
            return '';
        } elsif ($ident->[0] eq 'adjective') {
            return 'red';
        } elsif ($ident->[0] eq 'noun') {
            return 'fox';
        } elsif ($ident->[0] eq 'verb') {
            return 'jumped';
        } else {
            return '';
        }
    },
);

my $string = "The [% adjective %] [% noun %] [% verb %] over the river
+.\n";
$cet->process(\$string);
[download]




my @a=qw(random brilliant braindead); print $a[rand(@a)];

UNDEFINED_GET in this package appears to be able to do what I had in mind. I will have to take some time to play with it a bit. Thank you.