I'm facing the same problem

trying to do such things like :
${FILE:${ENV:INSTALL_DIR}/Success.html}

=> the result is : I see that the env variable is resolved but not the file

did a bit of digging, i believe the problem is here
RichTextPublisher.java (line 165)

Matcher matcher = FILE_VAR_PATTERN.matcher(text);
int start = 0;
while (matcher.find(start)) {
String fileName = matcher.group(2); <----- HERE
FilePath filePath = new FilePath(build.getWorkspace(), fileName);
if (filePath.exists()) {
String value = filePath.readToString();
if (matcher.group(1).length() != 4)

vars.put(String.format("%s:%s", matcher.group(1), fileName), value);
}
start = matcher.end();
}

can we do something like

String fileName = replaceVars(matcher.group(2), vars);

that might do the job, no?

The proposed change will not help. For the specified example:

${FILE:${ENV:INSTALL_DIR}/Success.html}

Captured group will be ${ENV:INSTALL_DIR which will not be parsed by replaceVars as you expect.

I see the support for nested expressions as a bad idea - it would be even possible to run into endless recursion if it is not done right.

What do you think if we allow constructs like:

${FILE:ENV:SOMEVAR}

which will be resolved into file content of the specified file?

@Dmitry
I think you should consider the usage of Token Macro Plugin