#!c:/perl/bin/perl -w
use strict;

my %data = (
  'bar' => {
    'code' => 'print $foo;',
    'values' => {
      'foo' => 'hello'
    }
  }
);

my $foo = 'hi';
eval $data{bar}{code};

if ($@) {
  $data{bar}{code} =~
    s/\$([^;]+);/\$data{bar}{values}{$1};/g;
  eval $data{bar}{code};
}