CkPython

SSH Commands to a Cisco Switch

Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending commands in a device console session. Each command is sent, and its output is read up to the device's next prompt.

Note: QuickShell allocates a PTY, which is what a network device console expects. The device presents an interactive prompt, and each command's output is read up to the next prompt.

Background: Network devices differ from general-purpose servers in that they expose a menu- or prompt-driven console rather than a Unix shell, so exec requests are usually unavailable and driving the interactive console is the only option. That makes prompt matching the synchronization mechanism, and it is why a PTY is appropriate here despite the general advice to avoid one. Retrieving the received text between commands is essential: a prompt left in the buffer would make the next receive return immediately with the wrong output.

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import sys
import chilkat

success = False

#  This example requires the Chilkat API to have been previously unlocked.
#  See Global Unlock Sample for sample code.

#  Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending
#  commands in a device console session.
#  
#  Note: QuickShell allocates a PTY, which is what a network device console expects.  The device
#  presents an interactive prompt, and each command's output is read up to the next prompt.

ssh = chilkat.CkSsh()

port = 22
success = ssh.Connect("172.16.16.100",port)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  Start a shell session.
channelNum = ssh.QuickShell()
if (channelNum < 0):
    print(ssh.lastErrorText())
    sys.exit()

#  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
#  which means no limit -- without it, this call waits forever if the received data never
#  contains a match.
ssh.put_ReadTimeoutMs(15000)

caseSensitive = True

#  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

cmdOutput = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(cmdOutput)

#  Send a command and read its output up to the next prompt.
success = ssh.ChannelSendString(channelNum,"show clock\n","utf-8")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  Retrieving the text also clears the receive buffer, which matters: if the prompt were left
#  buffered, the next receive would match it immediately and return the wrong output.
cmdOutput = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(cmdOutput)

#  Additional commands follow the same send / read-to-prompt / retrieve pattern.
success = ssh.ChannelSendString(channelNum,"show version\n","utf-8")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

cmdOutput = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(cmdOutput)

ssh.Disconnect()