Did you test this with -e -flag? I think that should work.
Such as echo -e "storePassword=test\n keyPassword=test\n keyAlias=test\\n storeFile=./upload-keystore.jks" > MyFile.txt
echo -e "storePassword=test\n keyPassword=test\n keyAlias=test\\n storeFile=./upload-keystore.jks" > MyFile.txt