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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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llSuccess = .F.

//  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.

loSsh = createobject("CkSsh")

lnPort = 22
llSuccess = loSsh.Connect("172.16.16.100",lnPort)
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

//  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.
lcPassword = "mySshPassword"

llSuccess = loSsh.AuthenticatePw("mySshLogin",lcPassword)
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

//  Start a shell session.
lnChannelNum = loSsh.QuickShell()
if (lnChannelNum < 0) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

//  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.
loSsh.ReadTimeoutMs = 15000

llCaseSensitive = .T.

//  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
llSuccess = loSsh.ChannelReceiveUntilMatch(lnChannelNum,"#","utf-8",llCaseSensitive)
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

lcCmdOutput = loSsh.GetReceivedText(lnChannelNum,"utf-8")
if (loSsh.LastMethodSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

? lcCmdOutput

//  Send a command and read its output up to the next prompt.
llSuccess = loSsh.ChannelSendString(lnChannelNum,"show clock" + Chr(10),"utf-8")
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

llSuccess = loSsh.ChannelReceiveUntilMatch(lnChannelNum,"#","utf-8",llCaseSensitive)
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

//  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.
lcCmdOutput = loSsh.GetReceivedText(lnChannelNum,"utf-8")
if (loSsh.LastMethodSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

? lcCmdOutput

//  Additional commands follow the same send / read-to-prompt / retrieve pattern.
llSuccess = loSsh.ChannelSendString(lnChannelNum,"show version" + Chr(10),"utf-8")
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

llSuccess = loSsh.ChannelReceiveUntilMatch(lnChannelNum,"#","utf-8",llCaseSensitive)
if (llSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

lcCmdOutput = loSsh.GetReceivedText(lnChannelNum,"utf-8")
if (loSsh.LastMethodSuccess = .F.) then
    ? loSsh.LastErrorText
    release loSsh
    return
endif

? lcCmdOutput

loSsh.Disconnect()


release loSsh