# load values into %config, template into $string, then...
1 while $string =~ s/\[%\s*(\S+)\s*%\]/$config{$1}/;

##</code><code>##

# load values into e.g. $CONFIG::variable1, etc., then...
$string = eval "package CONFIG;\n<<END_TEMPLATE;\n".$string."\nEND_TEMPLATE\n";