validate the substitution in test_exec.sh

scif/tests/test_exec.sh

@@ -6,4 +6,11 @@ echo "Testing exec of commands:"
 docker run -it "${CONTAINER_NAME}" exec hello-world-echo echo "Hello World!"
 docker run -it "${CONTAINER_NAME}" exec hello-world-script ls /
 docker run -it "${CONTAINER_NAME}" exec hello-world-env env
-docker run -it "${CONTAINER_NAME}" exec hello-world-env echo [e]OMG
+
+OUT=$(docker run -it "${CONTAINER_NAME}" --quiet exec hello-world-env echo [e]OMG | tr -d '\n\t\r ')
+if [ "$OUT" == "TACOS" ]; then
+   echo "Variable Substitution Success: $OUT"
+else
+   echo "Variable subsitution for e[OMG] failed"
+	 exit 1
+fi