A little ugly, but you could append:
";echo "I am a unique string that will not appear otherwise""
To your system call, then when you see this you can procede. That is if you cannot figure out how to get the prompt to print in non-interactive mode.
Scanning the tcsh man page (we don't have sh here...at least not in my man path), there is a -i switch that says:
-i The shell is interactive and prompts for its top-level input, even
+ if it appears to not be a terminal. Shells are interactive wi
+thout this option if their inputs and outputs are terminals.
Hope this helps!