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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use strict;
use warnings;
use Chilkat2;

# 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.

my $ssh = Chilkat2::Ssh->new;

my $sshPort = 22;
my $success = $ssh->Connect('ssh.example.com', $sshPort);
if (!$success) {
    print $ssh->LastErrorText, "\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.
my $password = 'mySshPassword';

$success = $ssh->AuthenticatePw('mySshLogin', $password);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

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

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

$success = $ssh->SendReqSetEnv($channelNum, 'MY_APP_MODE', 'production');
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Now run the command, which sees the requested environment.
$success = $ssh->SendReqExec($channelNum, 'echo $MY_APP_MODE');
if (!$success) {
    print $ssh->LastErrorText, "\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->ReadTimeoutMs(15000);

$success = $ssh->ChannelReceiveToClose($channelNum);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

my $output = $ssh->GetReceivedText($channelNum, 'utf-8');
if (!$ssh->LastMethodSuccess) {
    print $ssh->LastErrorText, "\n";
    exit;
}

print $output, "\n";

$ssh->Disconnect();