Objective-C

SSH Commands to a Cisco Switch

Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending commands in a device console session. Each command is sent, and its output is read up to the device's next prompt.

Note: QuickShell allocates a PTY, which is what a network device console expects. The device presents an interactive prompt, and each command's output is read up to the next prompt.

Background: Network devices differ from general-purpose servers in that they expose a menu- or prompt-driven console rather than a Unix shell, so exec requests are usually unavailable and driving the interactive console is the only option. That makes prompt matching the synchronization mechanism, and it is why a PTY is appropriate here despite the general advice to avoid one. Retrieving the received text between commands is essential: a prompt left in the buffer would make the next receive return immediately with the wrong output.

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Objective-C

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

BOOL success = NO;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending
//  commands in a device console session.
//  
//  Note: QuickShell allocates a PTY, which is what a network device console expects.  The device
//  presents an interactive prompt, and each command's output is read up to the next prompt.

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

int port = 22;
success = [ssh Connect: @"172.16.16.100" port: [NSNumber numberWithInt: port]];
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;
}

//  Start a shell session.
int channelNum = [[ssh QuickShell] intValue];
if (channelNum < 0) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

//  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
//  which means no limit -- without it, this call waits forever if the received data never
//  contains a match.
ssh.ReadTimeoutMs = [NSNumber numberWithInt:15000];

BOOL caseSensitive = YES;

//  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
success = [ssh ChannelReceiveUntilMatch: [NSNumber numberWithInt: channelNum] matchPattern: @"#" charset: @"utf-8" caseSensitive: caseSensitive];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

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

NSLog(@"%@",cmdOutput);

//  Send a command and read its output up to the next prompt.
success = [ssh ChannelSendString: [NSNumber numberWithInt: channelNum] strData: @"show clock\n" charset: @"utf-8"];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

success = [ssh ChannelReceiveUntilMatch: [NSNumber numberWithInt: channelNum] matchPattern: @"#" charset: @"utf-8" caseSensitive: caseSensitive];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

//  Retrieving the text also clears the receive buffer, which matters: if the prompt were left
//  buffered, the next receive would match it immediately and return the wrong output.
cmdOutput = [ssh GetReceivedText: [NSNumber numberWithInt: channelNum] charset: @"utf-8"];
if (ssh.LastMethodSuccess == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

NSLog(@"%@",cmdOutput);

//  Additional commands follow the same send / read-to-prompt / retrieve pattern.
success = [ssh ChannelSendString: [NSNumber numberWithInt: channelNum] strData: @"show version\n" charset: @"utf-8"];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

success = [ssh ChannelReceiveUntilMatch: [NSNumber numberWithInt: channelNum] matchPattern: @"#" charset: @"utf-8" caseSensitive: caseSensitive];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

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

NSLog(@"%@",cmdOutput);

[ssh Disconnect];