$template_file_string =~ s/\$(\w+)/${$1}/g;

##</code><code>##

my %vars = (
    title => 'Foo Bar'
);

my $template = q(<h1>$title</h1>);

$template =~ s/\$(\w+)/$vars{$1}/eg;

##</code><code>##

use Text::Template;

my %vars = (
    title => "Foo Bar"
);

my $t = new Text::Template(TYPE => 'STRING', SOURCE => q(<h1>{$title}</h1>))
    or die "Couldn't construct template: $Text::Template::ERROR";

my $text = $t->fill_in(HASH => \%vars);