如何使用libssh获取错误命令的输出

#include <libssh/libssh.h>
#include <stdio.h>

int main() {
    ssh_session session;
    int rc;

    // 创建SSH会话
    session = ssh_new();
    if (session == NULL) {
        printf("Failed to create SSH session.\n");
        return -1;
    }

    // 设置SSH连接参数
    ssh_options_set(session, SSH_OPTIONS_HOST, "remote_host");
    ssh_options_set(session, SSH_OPTIONS_PORT, "22");
    ssh_options_set(session, SSH_OPTIONS_USER, "username");
    ssh_options_set(session, SSH_OPTIONS_PASSWORD, "password");

    // 连接到远程服务器
    rc = ssh_connect(session);
    if (rc != SSH_OK) {
        printf("Failed to connect to remote server: %s\n", ssh_get_error(session));
        ssh_free(session);
        return -1;
    }

    // 执行命令
    ssh_channel channel;
    char buffer[256];
    int nbytes;

    channel = ssh_channel_new(session);
    if (channel == NULL) {
        printf("Failed to create SSH channel.\n");
        ssh_disconnect(session);
        ssh_free(session);
        return -1;
    }

    rc = ssh_channel_open_session(channel);
    if (rc != SSH_OK) {
        printf("Failed to open SSH channel: %s\n", ssh_get_error(session));
        ssh_channel_free(channel);
        ssh_disconnect(session);
        ssh_free(session);
        return -1;
    }

    rc = ssh_channel_request_exec(channel, "command");
    if (rc != SSH_OK) {
        printf("Failed to execute command: %s\n", ssh_get_error(session));
        ssh_channel_close(channel);
        ssh_channel_free(channel);
        ssh_disconnect(session);
        ssh_free(session);
        return -1;
    }

    // 获取命令输出
    nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
    if (nbytes < 0) {
        printf("Failed to read command output: %s\n", ssh_get_error(session));
        ssh_channel_close(channel);
        ssh_channel_free(channel);
        ssh_disconnect(session);
        ssh_free(session);
        return -1;
    }

    printf("Command output:\n%s\n", buffer);

    // 关闭SSH连接
    ssh_channel_send_eof(channel);
    ssh_channel_close(channel);
    ssh_channel_free(channel);
    ssh_disconnect(session);
    ssh_free(session);

    return 0;
}