Rust

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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// 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.

let ssh = chilkat::Ssh::new();

let ssh_port = 22;
if ssh.connect("ssh.example.com", ssh_port).is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

// 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.
let password = "mySshPassword".to_string();

if ssh.authenticate_pw("mySshLogin", &password).is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

// Open a session channel.  A negative return value indicates failure.
let channel_num = ssh.open_session_channel();
if channel_num < 0 {
    println!("{}", ssh.last_error_text());
    return;
}

// Set environment variables for the channel.  Multiple variables may be requested.
if ssh.send_req_set_env(channel_num, "LANG", "en_US.UTF-8").is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

if ssh.send_req_set_env(channel_num, "MY_APP_MODE", "production").is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

// Now run the command, which sees the requested environment.
if ssh.send_req_exec(channel_num, "echo $MY_APP_MODE").is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

// 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.set_read_timeout_ms(15000);

if ssh.channel_receive_to_close(channel_num).is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

let Ok(output) = ssh.get_received_text(channel_num, "utf-8") else {
    println!("{}", ssh.last_error_text());
    return;
};

println!("{}", output);

ssh.disconnect();