Variable substitution is a feature that was added to XML::Simple in version 2.04 (thanks mirod).

The way it works is that when your XML-format config file is read, any text of the for ${name} will be replaced with the value of the 'name' variable. You can define variables in your script using the Variables option or you can use the VarAttr option to define a special attribute name that is used to define variables in the config file itself.