A little ugly, but you could append:

";echo "I am a unique string that will not appear otherwise""
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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.
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Hope this helps!