It doesn't work because your regex is wrong. If you *really* wanted to do it using symbolic references, you'd want to use something like:

$template_file_string =~ s/\$(\w+)/${$1}/g;
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See the difference? You were matching "$title", then trying to substitute that with the value of the variable "$$title"--but that's not what you wanted. You want to just match the word part of the variable name ("title"), then substitute the whole thing with the value of "$title".

*However*, don't do it this way--there are better ways. One way is to put your template values into a hash, with the keys being the template variable names, and the values being the values that you want to substitute for the template variables; then use a regex to do the substitution.

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

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

$template =~ s/\$(\w+)/$vars{$1}/eg;
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Another (very) good option would be to use Text::Template.

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);
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This last is probably the most robust and extensible approach, so check it out. (Note that you have to slightly modify your template so that your variables are in '{}'.)