Lua

Set an Environment Variable on an SSH Channel

Demonstrates the Chilkat Ssh.SendReqSetEnv method, which asks the server to set an environment variable for a session channel. The arguments are the channel number, the variable name, and its value. Send these requests before the exec, shell, or subsystem request.

Background: This is the clean way to pass configuration to a remote command without embedding it in the command line. Be aware that many SSH servers restrict which variables clients may set (OpenSSH's AcceptEnv), so a request can be silently ignored or rejected — do not rely on it without verifying the server's policy.

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Lua

local chilkat = require("chilkat")

-- Demonstrates the Ssh.SendReqSetEnv method, which asks the server to set an environment
-- variable for a session channel.  The 1st argument is the channel number, the 2nd is the
-- variable name, and the 3rd is its value.  Send it before the exec, shell, or subsystem
-- request.

local ssh = chilkat.Ssh.new()

local sshPort = 22
local success = ssh:connect("ssh.example.com", sshPort)
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

-- Open a session channel.  A negative return value indicates failure.
local channelNum = ssh:open_session_channel()
if channelNum < 0 then
    print(ssh.last_error_text)
    return
end

-- Set environment variables for the channel.  Multiple variables may be requested.
success = ssh:send_req_set_env(channelNum, "LANG", "en_US.UTF-8")
if not success then
    print(ssh.last_error_text)
    return
end

success = ssh:send_req_set_env(channelNum, "MY_APP_MODE", "production")
if not success then
    print(ssh.last_error_text)
    return
end

-- Now run the command, which sees the requested environment.
success = ssh:send_req_exec(channelNum, "echo $MY_APP_MODE")
if not success then
    print(ssh.last_error_text)
    return
end

-- IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
-- it, this call waits forever if the server never sends channel close.
ssh.read_timeout_ms = 15000

success = ssh:channel_receive_to_close(channelNum)
if not success then
    print(ssh.last_error_text)
    return
end

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

print(output)

ssh:disconnect()