无法使用远程Shell更改目录

Question

I have been trying my hand at creating a remote shell in C for Unix. I am able to connect to the server and pull commands off of it. However I am unable to change my pwd, even though seems to operating correctly. I give it a directory and if that directory does not exist I will receive an error. Below is the quick shell I have been testing.

  while(1)
{

  for( n = 0; n < BUFFER_SIZE; n++)
{
  command[n] = '\0';
}

  write( sockfd, buffer, strlen( buffer ) );

  read( sockfd, command, BUFFER_SIZE );

  fprintf( stderr, "Command: %s\n", command );

  dup2(sockfd, 2);
  dup2(sockfd, 1);
  dup2(sockfd, 0);

   execlp( "/bin/sh", "sh", "-c", command, (char *)NULL );

}

Answer 1

cd is not a program, it is a shell builtin command, which changes the cwd for the shell, not for the program that spawned that shell. You are spawning a new shell for every command, so the changed cwd does not persist.

You could either try to catch invocations of cd and run chdir() yourself, or spawn a single interactive shell and use pipes or a pty (pseudo terminal) to communicate with it.

Answer 2

exec 'ing a cd command doesn't change the working directory of the program that calls exec . It forks a process that changes its own working directory, then exits.

You'll have to treat the cd command specially by invoking the chdir system call for it rather than exec .