You want symbolic references.

$writer->characters($$tag);
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But these are a really bad idea for very many reasons. In fact when you "use strict" (and I hope you use strict) symbolic references will trigger a fatal error.

You're better off using a hash.

$writer->characters($vars{$tag});
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--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg