Lua

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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Lua

local chilkat = require("chilkat")

-- 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.

local ssh = chilkat.Ssh.new()

local port = 22
local success = ssh:connect("172.16.16.100", port)
if not success then
    print(ssh.last_error_text)
    return
end

-- 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.
local password = "mySshPassword"

success = ssh:authenticate_pw("mySshLogin", password)
if not success then
    print(ssh.last_error_text)
    return
end

-- Start a shell session.
local channelNum = ssh:quick_shell()
if channelNum < 0 then
    print(ssh.last_error_text)
    return
end

-- 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.read_timeout_ms = 15000

local caseSensitive = true

-- The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
success = ssh:channel_receive_until_match(channelNum, "#", "utf-8", caseSensitive)
if not success then
    print(ssh.last_error_text)
    return
end

local cmdOutput = ssh:get_received_text(channelNum, "utf-8")
if not ssh.last_method_success then
    print(ssh.last_error_text)
    return
end

print(cmdOutput)

-- Send a command and read its output up to the next prompt.
success = ssh:channel_send_string(channelNum, "show clock\n", "utf-8")
if not success then
    print(ssh.last_error_text)
    return
end

success = ssh:channel_receive_until_match(channelNum, "#", "utf-8", caseSensitive)
if not success then
    print(ssh.last_error_text)
    return
end

-- 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:get_received_text(channelNum, "utf-8")
if not ssh.last_method_success then
    print(ssh.last_error_text)
    return
end

print(cmdOutput)

-- Additional commands follow the same send / read-to-prompt / retrieve pattern.
success = ssh:channel_send_string(channelNum, "show version\n", "utf-8")
if not success then
    print(ssh.last_error_text)
    return
end

success = ssh:channel_receive_until_match(channelNum, "#", "utf-8", caseSensitive)
if not success then
    print(ssh.last_error_text)
    return
end

cmdOutput = ssh:get_received_text(channelNum, "utf-8")
if not ssh.last_method_success then
    print(ssh.last_error_text)
    return
end

print(cmdOutput)

ssh:disconnect()