Lua

SSH Remote Shell with Multiple Commands

Demonstrates running several commands one after another in a single remote shell session, retrieving each command's output separately. No PTY is requested, so each command is followed by an echoed marker that signals where its output ends.

Background: Interleaving commands and reads in one shell requires a way to know where each command's output stops. An interactive session would use the shell prompt, but without a PTY the shell is non-interactive and never prints one — so the dependable technique is to append echo SOME_MARKER to each command and read up to that marker. Retrieving the text also clears the receive buffer, which matters here: if a marker were left buffered, the next receive would match it immediately and return the wrong output.

Chilkat Lua Downloads

Download Chilkat for Lua

Lua

local chilkat = require("chilkat")

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

-- Demonstrates running several commands one after another in a single remote shell session,
-- retrieving each command's output separately.
--
-- No PTY is requested, so the shell runs non-interactively and never prints a command prompt.
-- Because there is no prompt to synchronize on, each command is followed by an "echo" of a
-- unique marker, and the output is read up to that marker.

local ssh = chilkat.Ssh.new()

local hostname = "ssh.example.com"
local port = 22
local success = ssh:connect(hostname, 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

local channelNum = ssh:open_session_channel()
if channelNum < 0 then
    print(ssh.last_error_text)
    return
end

-- Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
-- raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
-- echo typed commands back, and skips interactive login scripts.  The output is therefore
-- clean and easily parseable -- but because no prompt is ever sent, code must not wait for
-- one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
success = ssh:send_req_shell(channelNum)
if not success 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

-- ---- 1st command: change directory ----
success = ssh:channel_send_string(channelNum, "cd /tmp; echo END_OF_CMD_1\n", "utf-8")
if not success then
    print(ssh.last_error_text)
    return
end

success = ssh:channel_receive_until_match(channelNum, "END_OF_CMD_1", "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 next marker were
-- left in the buffer, the following receive would match immediately.
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)

-- ---- 2nd command: directory listing ----
success = ssh:channel_send_string(channelNum, "ls; echo END_OF_CMD_2\n", "utf-8")
if not success then
    print(ssh.last_error_text)
    return
end

success = ssh:channel_receive_until_match(channelNum, "END_OF_CMD_2", "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)

-- ---- 3rd command: long listing, then finish the session ----
success = ssh:channel_send_string(channelNum, "ls -l\n", "utf-8")
if not success then
    print(ssh.last_error_text)
    return
end

-- No more input will be sent.
success = ssh:channel_send_eof(channelNum)
if not success then
    print(ssh.last_error_text)
    return
end

success = ssh:channel_receive_to_close(channelNum)
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()