Seeking means to get Fabric to automatically (instead of user-interactively) interact with shell commands (and not just requests for passwords, but also requested user input when no "stdin/interactive override" like apt-get install -y is available).
This question along with these Fabric docs suggest that Fabric can only "push the interactivity" back to the human user that's running the Fabric program. Seeking to instead fully automate without any human presence. Don't yet have a "real," current problem to solve, just preparing for possible, future obstacle.
Possibly useful to combine with pexpect (or similar, alternative mechanism) if Fabric can't exclusively handle all stdin/prompts automatically? Hoping it doesn't need to be an "either/or" kind of thing. Why not leverage both (pexpect and Fabric) where appropriate, if applicable, in same program/automation?
As Glenn, I would say use pexpect; in addition,
have a look at this wrapper I wrote to script the pexpect behaviour from fabric:
from ilogue.fexpect import expect, expecting, run
prompts = []
prompts += expect('What is your name?','John')
prompts += expect('Where do you live?','New York')
with expecting(prompts):
run('command')
See also my blogpost on fexpect or how to handle prompts in fabric with pexpect