Hello!
With gcloud preview app deploy now performing a remote build by default, the command does not respect gcloud --quiet anymore.
According to the usage output of gcloud, the option --quiet should "Disable all interactive prompts."
gcloud --quiet preview app deploy ... will in some cases ask for a passphrase when generating some SSH key. This breaks scripts that depend on --quiet, i.e. do not provide input to gcloud.
A workaround is sending "\n\n" to standard input, but that's extremely ugly.
Lorenz