I did something similar with a project for Node.js called nermal[1], which comes with an example called `tagaloop` that I still use to store my passwords. Even though it had a bit larger of a scope (it is a library for encrypting/decrypting arbitrary JSON with AES-GCM + scrypt + random-length-padding), one of the examples is a password manager called `tagaloop`. It did not really get the sort of traction that I hope you're going to see -- good luck! Fortunately I can still call it a success because it has made
my life much easier in many cases.
We both can make different choices and that's OK, but I'm happy to see as a design point that both of our password managers are interactive loops to avoid the history management of the shell. I will say, though, that my files routinely hold way more than 4 passwords and listing them all for the user to choose by number is not really appealing: so one of the biggest things that `tagaloop` does is that it just lets you grep through them at the interactive console. You might want to consider that as a very important feature.
[1] https://github.com/drostie/nermal