Can a process group variable reference another variables?

[#1]

Is the following a valid way to define variables? In other words can the expression language be used to compute one variable from another?

[#2]

If I cant set attributes on this fashion, can I somehow use UpdateAttribute to pass an attribute into a process group? The process group does not have a flowfile as an input. So I'm not sure how to do this..

[#3]

@David Sargrad

You can use Nifi custom properties file for this case and add new property in nifi.properties and give your custom property file path, then restart NiFi instance then you can refer the variables.

if you add variable in NiFi UI then they are evaluate as literal values if you already have the attribute name in custom properties file then only you will get the values for the attribute or else they are going to be literals(i.e ${DST_WWW_FOLDER}).

Another way of doing make use NiFi restapi to update (or) add new variable in variable registry by using HTTP processors to make api call.