How to read router prompt and use it?

[simbha]

When i login to a router, i get a following prompt.

R3-NYC
login: tac
Password:
[Router]R3-NYC#
[Router]R3-NYC#show clock
Wed May 22 04:46:18 2019 CST
[Router]R3-NYC#

1. How to capture CLI prompt to a string variable and use it for read_until() ?
i want to capture the prompt "[Router]R3-NYC#" . If i use read_until(), i have to mention the match. But i want to capture it after i login and use it later for the read_until() function the entire string instead of partial matches. I cannot hard core the hostname because i use this function for several other devices which will have different prompts.

2. How to capture command output to a string ?
I saw many refering to the function read_eager(). For some reason, when i test it, it has no capture. Only read_all() is working as expected. For this i have to wait till the telnet is closed. Could you please share some examples, if read_eager() is working for you.

Thanks
Simbha