test: different grep method

Author: andhreljaKern

pi/edit_dockerfile.sh

@@ -19,7 +19,9 @@ do
     esac
 done
 
-PI_EXISTING_TAG=$(grep "${DOCKER_REGISTRY}/${PARENT_IMAGE_NAME}:" $DOCKERFILE | sed 's|FROM ||g' | cut -d ':' -f 2)
+line=$(grep "${DOCKER_REGISTRY}/${PARENT_IMAGE_NAME}:" $DOCKERFILE)
+
+PI_EXISTING_TAG=$(echo $line | sed 's|FROM ||g' | cut -d ':' -f 2)
 PI_EXISTING_IMAGE="${DOCKER_REGISTRY}/${PARENT_IMAGE_NAME}:${PI_EXISTING_TAG}"
 PI_NEW_IMAGE="${DOCKER_REGISTRY}/${PARENT_IMAGE_NAME}:${RELEASE_TAG}-${PARENT_IMAGE_TYPE}"