Objective-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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Objective-C

#import <CkoSsh.h>
#import <NSString.h>

BOOL success = NO;

//  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.

CkoSsh *ssh = [[CkoSsh alloc] init];

int sshPort = 22;
success = [ssh Connect: @"ssh.example.com" port: [NSNumber numberWithInt: sshPort]];
if (success == NO) {
    NSLog(@"%@",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.
NSString *password = @"mySshPassword";

success = [ssh AuthenticatePw: @"mySshLogin" password: password];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

//  Open a session channel.  A negative return value indicates failure.
int channelNum = [[ssh OpenSessionChannel] intValue];
if (channelNum < 0) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

//  Set environment variables for the channel.  Multiple variables may be requested.
success = [ssh SendReqSetEnv: [NSNumber numberWithInt: channelNum] name: @"LANG" value: @"en_US.UTF-8"];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

success = [ssh SendReqSetEnv: [NSNumber numberWithInt: channelNum] name: @"MY_APP_MODE" value: @"production"];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

//  Now run the command, which sees the requested environment.
success = [ssh SendReqExec: [NSNumber numberWithInt: channelNum] command: @"echo $MY_APP_MODE"];
if (success == NO) {
    NSLog(@"%@",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 = [NSNumber numberWithInt:15000];

success = [ssh ChannelReceiveToClose: [NSNumber numberWithInt: channelNum]];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

NSString *output = [ssh GetReceivedText: [NSNumber numberWithInt: channelNum] charset: @"utf-8"];
if (ssh.LastMethodSuccess == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

NSLog(@"%@",output);

[ssh Disconnect];