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SSH Exec (Execute Command Line)

Demonstrates running a single command on an SSH server with an exec request and retrieving its output. The example connects, authenticates, opens a session channel, sends the command, reads until the server closes the channel, and then checks the exit status.

Background: exec is the workhorse of SSH automation: it runs one command and the server closes the channel when the command exits, which is a definitive end-of-output signal. No PTY is involved, so the shell runs non-interactively — no prompt, no echoed input, no ANSI escape codes — giving clean, parseable output. Remember that an accepted exec request only means the request was accepted; the command's own success is reported through the channel exit status. Command syntax depends on the remote shell, which is the user's default shell on Linux/UNIX and usually CMD.EXE on Windows SSH servers.

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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

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

    // Demonstrates running a single command on an SSH server with an exec request and retrieving
    // its output.  An exec request runs one command and the server closes the channel when it
    // finishes -- no PTY and no shell prompt are involved, so the output is clean and parseable.

    const ssh = try chilkat.Ssh.init();
    defer ssh.deinit();

    // The hostname may be a hostname or an IP address.
    const hostname = "ssh.example.com";
    const port = 22;
    ssh.connect(hostname, port) catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        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.
    const password = "mySshPassword";

    ssh.authenticatePw("mySshLogin", password) catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    // Open a session channel.  Several session channels may be open at once on one connection.
    const channel_num = ssh.openSessionChannel();
    if (channel_num < 0) {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    }

    // The command syntax depends on the remote system's shell.  On Linux/UNIX it is typically the
    // user's default shell; on Windows SSH servers it is usually CMD.EXE.
    //   Linux/UNIX:  "ls -l /tmp"        or  "cd /etc; ls -la"
    //   Windows:     "dir"               or  "\"cd \\temp&&dir\""
    ssh.sendReqExec(channel_num, "ls -l /tmp") catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        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.setReadTimeoutMs(15000);

    // Read the output until the server sends channel close, which happens when the command exits.
    ssh.channelReceiveToClose(channel_num) catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    const cmd_output = ssh.getReceivedText(alloc, channel_num, "utf-8") catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("{s}\n", .{cmd_output});

    // An accepted exec request does not mean the command succeeded.  Check the exit status.
    if (ssh.channelReceivedExitStatus(channel_num)) {
        std.debug.print("Exit status: {d}\n", .{ssh.getChannelExitStatus(channel_num)});
    }

    ssh.disconnect();
}