Escaping ${} in NAnt Scripts

Today I was writing a NAnt script that calls an XSLT, passing in some regular expression replacement arguments so I could use replace occurrences of certain strings in an XML file. The problem I ran into is that the syntax for a regex replacement is ${group}, which is exactly the same as the syntax for a property in a NAnt script. I figured there must be an escape sequence in NAnt that lets you say, “No, I really want a dollar sign and a curly brace - I'm not specifying a property.“ But I tried backslash and the other usual suspects, then searched the web for a while. Nothing.

I banged my head against the problem for a while, and finally came up with this:

<property name="replacement" value="http://localhost/${product.name}-${websafe.version}${'${path}'}" />

It's the ${'${path}'} that actually does the trick: basically, I'm saying, “Use the string literal ${path}.“

I'm pretty sure this will only work in NAnt 0.85 and later, as that's when string literal expressions were introduced.