Approaches to bash scripting (passing variables from OS to Caché)

Let's say I want to execute  this cache script (saved as test.txt) from OS terminal:

zn "USER"
write 1
zn "%SYS"
write 2
halt

Executing the following command in a terminal:

csession cache < test.txt

Would yield this output:

$ csession cache < script.txt

Node: gitlab-test, Instance: CACHE

USER>

USER>
1
USER>

%SYS>
2
%SYS>
Job succeeded

Is there a better way to run these scripts?

Currently I have two problems:

1. I have several variables defined in my bash script, what's the best approach to pass them into Caché? 
2. I can't capture script input (for example write 1)

As for 1 there are two solutions I found:

1. Generate test.txt dynamically from bash. That way I can just hardcode variables, but I don't really like this approach because writing a script that generates another script and executes it is non-trivial, also parent script is hard to read.
2. Use  $system.Util.GetEnviron("EnvVar") to get variables from Cache side. It works, but maybe there are  other, better approaches?

No ideas so far for 2 though.