Swift

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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func chilkatTest() {
    var success: Bool = 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.

    let ssh = CkoSsh()!

    var sshPort: Int = 22
    success = ssh.connect(hostname: "ssh.example.com", port: sshPort)
    if success == false {
        print("\(ssh.lastErrorText!)")
        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.
    var password: String? = "mySshPassword"

    success = ssh.authenticatePw(login: "mySshLogin", password: password)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  Open a session channel.  A negative return value indicates failure.
    var channelNum: Int = ssh.openSessionChannel().intValue
    if channelNum < 0 {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  Set environment variables for the channel.  Multiple variables may be requested.
    success = ssh.sendReqSetEnv(channelNum: channelNum, name: "LANG", value: "en_US.UTF-8")
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    success = ssh.sendReqSetEnv(channelNum: channelNum, name: "MY_APP_MODE", value: "production")
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  Now run the command, which sees the requested environment.
    success = ssh.sendReqExec(channelNum: channelNum, command: "echo $MY_APP_MODE")
    if success == false {
        print("\(ssh.lastErrorText!)")
        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.readTimeoutMs = 15000

    success = ssh.channelReceive(toClose: channelNum)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    var output: String? = ssh.getReceivedText(channelNum: channelNum, charset: "utf-8")
    if ssh.lastMethodSuccess == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    print("\(output!)")

    ssh.disconnect()

}