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doc/command.dox
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Jakub Jelen
CVE-2025-4878 Initialize pointers where possible
23 июн 2025, 16:24
23 июн 2025, 16:242eb2af4
/**
@page libssh_tutor_command Chapter 4: Passing a remote command
@section remote_command Passing a remote command

Previous chapter has shown how to open a full shell session, with an attached
terminal or not. If you only need to execute a command on the remote end,
you don't need all that complexity.

The method described here is suited for executing only one remote command.
If you need to issue several commands in a row, you should consider using
a non-interactive remote shell, as explained in previous chapter.

@see shell


@subsection exec_remote Executing a remote command

The first steps for executing a remote command are identical to those
for opening remote shells. You first need a SSH channel, and then
a SSH session that uses this channel:

@code
int show_remote_files(ssh_session session)
{
  ssh_channel channel = NULL;
  int rc;

  channel = ssh_channel_new(session);
  if (channel == NULL) return SSH_ERROR;

  rc = ssh_channel_open_session(channel);
  if (rc != SSH_OK)
  {
    ssh_channel_free(channel);
    return rc;
  }
@endcode

Once a session is open, you can start the remote command with
ssh_channel_request_exec():

@code
  rc = ssh_channel_request_exec(channel, "ls -l");
  if (rc != SSH_OK)
  {
    ssh_channel_close(channel);
    ssh_channel_free(channel);
    return rc;
  }
@endcode

If the remote command displays data, you get them with ssh_channel_read().
This function returns the number of bytes read. If there is no more
data to read on the channel, this function returns 0, and you can go to next step.
If an error has been encountered, it returns a negative value:

@code
  char buffer[256];
  int nbytes;

  nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
  while (nbytes > 0)
  {
    if (fwrite(buffer, 1, nbytes, stdout) != nbytes)
    {
      ssh_channel_close(channel);
      ssh_channel_free(channel);
      return SSH_ERROR;
    }
    nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
  }

  if (nbytes < 0)
  {
    ssh_channel_close(channel);
    ssh_channel_free(channel);
    return SSH_ERROR;
  }
@endcode

Once you read the result of the remote command, you send an
end-of-file to the channel, close it, and free the memory
that it used:

@code
  ssh_channel_send_eof(channel);
  ssh_channel_close(channel);
  ssh_channel_free(channel);

  return SSH_OK;
}
@endcode

Warning: In a single channel, only ONE command can be executed!
If you want to executed multiple commands, allocate separate channels for
them or consider opening interactive shell.
Attempting to run multiple consecutive commands in one channel will fail.


*/