If a property foo is defined, the string

  ${foo}

is replaced by the value of foo inside an ant
build script.

How can I pass the string literally, without
substitution, to an ant task? Example:
I want to replace all occurences of the string

  ${abc}

by

  ${xyz}

in a file. Using

<replace file="..." token="${abc}" value="${xyz}" />

does not work, because the property values of abc and
xyz are substituted, before replace is executed.

I need a way to *escape* the property substitution
mechanism of Ant.

Ronald