Excluding files from the release bundle using a script

I have some files that I need when the application is in develop mode but want to exclude on the release version.

I have added this script to the build phase

if [ ${CONFIGURATION} == "Release" ]; then
rm -rf ${BUILT_PRODUCTS_DIR}/${PRODUCT_NAME}.app/CORE_DATA_IMAGE/
fi

CORE_DATA_IMAGE is a directory that contains a lot of images that I don't want on the release version.

This script is doing exactly nothing. The images continue to be included on the final release version.

Any ideas?