Perl

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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Perl

use chilkat();

$success = 0;

#  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.

$ssh = chilkat::CkSsh->new();

$sshPort = 22;
$success = $ssh->Connect("ssh.example.com",$sshPort);
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

#  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.
$password = "mySshPassword";

$success = $ssh->AuthenticatePw("mySshLogin",$password);
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

#  Open a session channel.  A negative return value indicates failure.
$channelNum = $ssh->OpenSessionChannel();
if ($channelNum < 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

#  Set environment variables for the channel.  Multiple variables may be requested.
$success = $ssh->SendReqSetEnv($channelNum,"LANG","en_US.UTF-8");
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

$success = $ssh->SendReqSetEnv($channelNum,"MY_APP_MODE","production");
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

#  Now run the command, which sees the requested environment.
$success = $ssh->SendReqExec($channelNum,"echo $MY_APP_MODE");
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

#  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 == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

$output = $ssh->getReceivedText($channelNum,"utf-8");
if ($ssh->get_LastMethodSuccess() == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

print $output . "\r\n";

$ssh->Disconnect();