Pexpect and SSH

If you try to use the previous Telnet example and plug it into an SSH session instead, you might find yourself pretty frustrated with the experience. You always have to include the username in the session, answering the ssh new key question, and much more mundane tasks. There are many ways to make SSH sessions work, but luckily, Pexpect has a subclass called pxssh, which specializes in setting up SSH connections. The class adds methods for login, log out, and various tricky things to handle the different situations in the ssh login process. The procedures are mostly the same, with the exception of login() and logout():

>>> from pexpect import pxssh
>>> child = pxssh.pxssh()
>>> child.login('172.16.1.20', 'cisco', 'cisco', auto_prompt_reset=False)
True
>>> child.sendline('show version | i V')
19
>>> child.expect('iosv-1#')
0
>>> child.before
b'show version | i VrnCisco IOS Software, IOSv Software (VIOS-ADVENTERPRISEK9-M), Version 15.6(2)T, RELEASE SOFTWARE (fc2)rnProcessor board ID 9MM4BI7B0DSWK40KV1IIRrn'
>>> child.logout()
>>>

Notice the auto_prompt_reset=False argument in the login() method. By default, pxssh uses the Shell prompt to synchronize the output. But since it uses the PS1 option for most of bash or CSH, they will error out on Cisco or other network devices.