I am writing a bash script on a machine without expect. The script automates the build of a helm (v2.9.1) chart.

I've got to the part in the script where it runs a

helm package --sign --key 'mykey' --keyring 'path/to/keyring' -d chartdir chart

and because helm prompts for the passphrase of the gpg key I created in order to use provenance files (a requirement), I cannot script around the soliciting of the passphrase, which I would like to prompt for separately as the script is part of a CI/CD build chain.

I have tried using

yes $promptedPassPhrase | helm package --sign...

and I got

xrealloc: cannot allocate 18446744071562067968 bytes (237568 bytes allocated)

I also tried plain old

echo $promptedPassPhrase | helm package --sign...

and I got

Error: inappropriate ioctl for device

I also tried script and got the same response. As I do not have expect on the server, I cannot expect my way round it, so I'm stumped as to how to automate the helm package command and am not going to use a key without a passphrase as it is bad practice.