Using espruino non-interactively

If you mean using Espruino directly from C code, you want something like:

JsVar *v = jsvNewFromString("......");
jsvUnLock(jspEvaluateVar(jsiGetParser(), lineToExecute, 0));
jsvUnLock(v);

Note that EvaluateVar returns a result as well.

Espruino can't execute directly from char* strings (only from JsVar-based strings).