首先，libssh2.lib的这个库一定要有（下载地址提供：http://download.csdn.net/detail/wyc6668205/5651661） 其次，介绍一下libssh2的官网：www.libssh2.org；虽然这个网站里面内容是全英文的，我想所有的计算机从事者都能看懂这里面写的内容，这里面提供了

首先，libssh2.lib的这个库一定要有（下载地址提供：http://download.csdn.net/detail/wyc6668205/5651661）

其次，介绍一下libssh2的官网：www.libssh2.org；虽然这个网站里面内容是全英文的，我想所有的计算机从事者都能看懂这里面写的内容，这里面提供了很多例子，比如FTP的，shell命令的等等，我在这里介绍一下shell命令的发送和接收返回数据。

example里有个文件名叫exec.c 这个文件是实现shell命令的一个例子

/*
 * Sample showing how to use libssh2 to execute a command remotely.
 *
 * The sample code has fixed values for host name, user name, password
 * and command to run.
 *
 * Run it like this:
 *
 * $ ./ssh2_exec 127.0.0.1 user password "uptime"
 *
 */ 
 
#include "libssh2_config.h"
#include 
 
#ifdef HAVE_WINSOCK2_H
#include 
#endif
#ifdef HAVE_SYS_SOCKET_H
#include 
#endif
#ifdef HAVE_NETINET_IN_H
#include 
#endif
#ifdef HAVE_SYS_SELECT_H
#include 
#endif
#ifdef HAVE_UNISTD_H
#include 
#endif
#ifdef HAVE_ARPA_INET_H
#include 
#endif
 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
 
static int waitsocket(int socket_fd, LIBSSH2_SESSION *session)
{
 struct timeval timeout;
 int rc;
 fd_set fd;
 fd_set *writefd = NULL;
 fd_set *readfd = NULL;
 int dir;
 
 timeout.tv_sec = 10;
 timeout.tv_usec = 0;
 
 FD_ZERO(&fd);
 
 FD_SET(socket_fd, &fd);
 
 /* now make sure we wait in the correct direction */ 
 dir = libssh2_session_block_directions(session);

 
 if(dir & LIBSSH2_SESSION_BLOCK_INBOUND)
 readfd = &fd;
 
 if(dir & LIBSSH2_SESSION_BLOCK_OUTBOUND)
 writefd = &fd;
 
 rc = select(socket_fd + 1, readfd, writefd, NULL, &timeout);
 
 return rc;
}
 
int main(int argc, char *argv[])
{
 const char *hostname = "127.0.0.1";
 const char *commandline = "uptime";
 const char *username = "user";
 const char *password = "password";
 unsigned long hostaddr;
 int sock;
 struct sockaddr_in sin;
 const char *fingerprint;
 LIBSSH2_SESSION *session;
 LIBSSH2_CHANNEL *channel;
 int rc;
 int exitcode;
 char *exitsignal=(char *)"none";
 int bytecount = 0;
 size_t len;
 LIBSSH2_KNOWNHOSTS *nh;
 int type;
 
#ifdef WIN32
 WSADATA wsadata;
 WSAStartup(MAKEWORD(2,0), &wsadata);
#endif
 if (argc > 1)
 /* must be ip address only */ 
 hostname = argv[1];
 
 if (argc > 2) {
 username = argv[2];
 }
 if (argc > 3) {
 password = argv[3];
 }
 if (argc > 4) {
 commandline = argv[4];
 }
 
 rc = libssh2_init (0);

 if (rc != 0) {
 fprintf (stderr, "libssh2 initialization failed (%d)\n", rc);
 return 1;
 }
 
 hostaddr = inet_addr(hostname);
 
 /* Ultra basic "connect to port 22 on localhost"
 * Your code is responsible for creating the socket establishing the
 * connection
 */ 
 sock = socket(AF_INET, SOCK_STREAM, 0);
 
 sin.sin_family = AF_INET;
 sin.sin_port = htons(22);
 sin.sin_addr.s_addr = hostaddr;
 if (connect(sock, (struct sockaddr*)(&sin),
 sizeof(struct sockaddr_in)) != 0) {
 fprintf(stderr, "failed to connect!\n");
 return -1;
 }
 
 /* Create a session instance */ 
 session = libssh2_session_init();

 if (!session)
 return -1;
 
 /* tell libssh2 we want it all done non-blocking */ 
 libssh2_session_set_blocking(session, 0);

 
 /* ... start it up. This will trade welcome banners, exchange keys,
 * and setup crypto, compression, and MAC layers
 */ 
 while ((rc = libssh2_session_handshake(session, sock)) ==

 LIBSSH2_ERROR_EAGAIN);
 if (rc) {
 fprintf(stderr, "Failure establishing SSH session: %d\n", rc);
 return -1;
 }
 
 nh = libssh2_knownhost_init(session);

 if(!nh) {
 /* eeek, do cleanup here */ 
 return 2;
 }
 
 /* read all hosts from here */ 
 libssh2_knownhost_readfile(nh, "known_hosts",

 LIBSSH2_KNOWNHOST_FILE_OPENSSH);
 
 /* store all known hosts to here */ 
 libssh2_knownhost_writefile(nh, "dumpfile",

 LIBSSH2_KNOWNHOST_FILE_OPENSSH);
 
 fingerprint = libssh2_session_hostkey(session, &len, &type);

 if(fingerprint) {
 struct libssh2_knownhost *host;
#if LIBSSH2_VERSION_NUM >= 0x010206
 /* introduced in 1.2.6 */ 
 int check = libssh2_knownhost_checkp(nh, hostname, 22,

 fingerprint, len,
 LIBSSH2_KNOWNHOST_TYPE_PLAIN|
 LIBSSH2_KNOWNHOST_KEYENC_RAW,
 &host);
#else
 /* 1.2.5 or older */ 
 int check = libssh2_knownhost_check(nh, hostname,

 fingerprint, len,
 LIBSSH2_KNOWNHOST_TYPE_PLAIN|
 LIBSSH2_KNOWNHOST_KEYENC_RAW,
 &host);
#endif
 fprintf(stderr, "Host check: %d, key: %s\n", check,
 (check <= LIBSSH2_KNOWNHOST_CHECK_MISMATCH)?
 host->key:"");
 
 /*****
 * At this point, we could verify that 'check' tells us the key is
 * fine or bail out.
 *****/ 
 }
 else {
 /* eeek, do cleanup here */ 
 return 3;
 }
 libssh2_knownhost_free(nh);

 
 if ( strlen(password) != 0 ) {
 /* We could authenticate via password */ 
 while ((rc = libssh2_userauth_password(session, username, password)) ==

 LIBSSH2_ERROR_EAGAIN);
 if (rc) {
 fprintf(stderr, "Authentication by password failed.\n");
 goto shutdown;
 }
 }
 else {
 /* Or by public key */ 
 while ((rc = libssh2_userauth_publickey_fromfile(session, username,

 "/home/user/"
 ".ssh/id_rsa.pub",
 "/home/user/"
 ".ssh/id_rsa",
 password)) ==
 LIBSSH2_ERROR_EAGAIN);
 if (rc) {
 fprintf(stderr, "\tAuthentication by public key failed\n");
 goto shutdown;
 }
 }
 
#if 0
 libssh2_trace(session, ~0 );

#endif
 
 /* Exec non-blocking on the remove host */ 
 while( (channel = libssh2_channel_open_session(session)) == NULL &&

 libssh2_session_last_error(session,NULL,NULL,0) ==

 LIBSSH2_ERROR_EAGAIN )
 {
 waitsocket(sock, session);
 }
 if( channel == NULL )
 {
 fprintf(stderr,"Error\n");
 exit( 1 );
 }
 while( (rc = libssh2_channel_exec(channel, commandline)) ==

 LIBSSH2_ERROR_EAGAIN )
 {
 waitsocket(sock, session);
 }
 if( rc != 0 )
 {
 fprintf(stderr,"Error\n");
 exit( 1 );
 }
 for( ;; )
 {
 /* loop until we block */ 
 int rc;
 do
 {
 char buffer[0x4000];
 rc = libssh2_channel_read( channel, buffer, sizeof(buffer) );

 if( rc > 0 )
 {
 int i;
 bytecount += rc;
 fprintf(stderr, "We read:\n");
 for( i=0; i < rc; ++i )
 fputc( buffer[i], stderr);
 fprintf(stderr, "\n");
 }
 else {
 if( rc != LIBSSH2_ERROR_EAGAIN )
 /* no need to output this for the EAGAIN case */ 
 fprintf(stderr, "libssh2_channel_read returned %d\n", rc);
 }
 }
 while( rc > 0 );
 
 /* this is due to blocking that would occur otherwise so we loop on
 this condition */ 
 if( rc == LIBSSH2_ERROR_EAGAIN )
 {
 waitsocket(sock, session);
 }
 else
 break;
 }
 exitcode = 127;
 while( (rc = libssh2_channel_close(channel)) == LIBSSH2_ERROR_EAGAIN )

 waitsocket(sock, session);
 
 if( rc == 0 )
 {
 exitcode = libssh2_channel_get_exit_status( channel );

 libssh2_channel_get_exit_signal(channel, &exitsignal,

 NULL, NULL, NULL, NULL, NULL);
 }
 
 if (exitsignal)
 fprintf(stderr, "\nGot signal: %s\n", exitsignal);
 else
 fprintf(stderr, "\nEXIT: %d bytecount: %d\n", exitcode, bytecount);
 
 libssh2_channel_free(channel);

 channel = NULL;
 
shutdown:
 
 libssh2_session_disconnect(session,

 "Normal Shutdown, Thank you for playing");
 libssh2_session_free(session);

 
#ifdef WIN32
 closesocket(sock);
#else
 close(sock);
#endif
 fprintf(stderr, "all done\n");
 
 libssh2_exit();

 
 return 0;
}

1.WSAStartup()，打开socket链接库

2.socket()，初始化一个socket套接字

3.connect()，连接到ssh服务器

4.libssh2_session_init()，初始化一个ssh连接

5.libssh2_session_handshake()，将socket和session握手通信

6.libssh2_userauth_password()，验证登陆

7.libssh2_channel_open_session()，打开通道

8.libssh2_channel_exec()，发送shell命令

9.libssh2_channel_read()，读取命令处理结果

这里的8.libssh2_channel_exec()，发送shell命令和心目中想象的不太一样，不能循环发送命令，发送第一次命令时，该命令执行，但是第二次再发送时会返回一个

名字叫LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED的ERROR，也就是说这个函数只能发送一次shell命令就不能再用了，太麻烦了。

在这里这种需求怎么解决：

当调用完libssh2_channel_exec()时，将通道释放掉libssh2_channel_close()，然后再重新打开libssh2_channel_open()，再使用这个libssh2_channel_exec()发送shell命令。

但是在这里可能会出现一个问题，在libssh2_channel_open()的时候并没有把通道打开，调用libssh2_session_last_error()发现这个错误代码是LIBSSH2_ERROR_EAGAIN，在官方网站的解释是这不是一个错误，是一个阻塞的过程，也就是现在这个链接已经阻塞了，需要等等再打开。这也就是最上面那个waitsocket()的作用了。