C++

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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C++

#include <CkSsh.h>

void ChilkatSample(void)
    {
    bool success = false;

    //  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.

    CkSsh ssh;

    int sshPort = 22;
    success = ssh.Connect("ssh.example.com",sshPort);
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        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.
    const char *password = "mySshPassword";

    success = ssh.AuthenticatePw("mySshLogin",password);
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    //  Open a session channel.  A negative return value indicates failure.
    int channelNum = ssh.OpenSessionChannel();
    if (channelNum < 0) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    //  Set environment variables for the channel.  Multiple variables may be requested.
    success = ssh.SendReqSetEnv(channelNum,"LANG","en_US.UTF-8");
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    success = ssh.SendReqSetEnv(channelNum,"MY_APP_MODE","production");
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    //  Now run the command, which sees the requested environment.
    success = ssh.SendReqExec(channelNum,"echo $MY_APP_MODE");
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        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.put_ReadTimeoutMs(15000);

    success = ssh.ChannelReceiveToClose(channelNum);
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    const char *output = ssh.getReceivedText(channelNum,"utf-8");
    if (ssh.get_LastMethodSuccess() == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    std::cout << output << "\r\n";

    ssh.Disconnect();
    }