[lug] reference/tutorial for connecting to port 23

[Alan Robertson]

matthew.w.mcillece at lmco.com wrote:
> 
> Does anyone know where I might find an explanation of how to automatically
> pass the output of a distinct process to (and through) a connection such as
> telnet?  I've always expected telnet to be tied to the keyboard that
> initiated the connection, but now need to pass characters generated by
> another process through without user intervention, if possible.  I've been
> reading an IRIX Network Programming Guide but the discussion is not what I
> can use.  I've also grepped through all the Linux HOWTO's, but haven't found
> anything quite on topic.

Here's some GPLed code I wrote a week or so ago to do that: 
/*
 * Start a process with its stdin and stdout redirected to pipes
 * so the parent process can talk to it.
 */
int
StartProcess(const char * cmd, int * readfd, int * writefd)
{
        pid_t   pid;
        int     wrpipe[2];      /* The pipe the parent process writes to */
                                /* (which the child process reads from) */
        int     rdpipe[2];      /* The pipe the parent process reads from */
                                /* (which the child process writes to) */
 
        if (pipe(wrpipe) < 0) {
                perror("cannot create pipe\n");
                return(-1);
        }
        if (pipe(rdpipe) < 0) {
                perror("cannot create pipe\n");
                close(wrpipe[0]);
                close(wrpipe[1]);
                return(-1);
        }
        switch(pid=fork()) {
 
                case -1:        perror("cannot StartProcess cmd");
                                close(rdpipe[0]);
                                close(wrpipe[1]);
                                close(wrpipe[0]);
                                close(rdpipe[1]);
                                return(-1);
 
                case 0:         /* We are the child */
 
                                /* Redirect stdin */
                                close(0);
                                dup2(wrpipe[0], 0);
                                close(wrpipe[0]);
                                close(wrpipe[1]);
 
                                /* Redirect stdout */
                                close(1);
                                dup2(rdpipe[1], 1);
                                close(rdpipe[0]);
                                close(rdpipe[1]); 
                  
                                execlp("/bin/sh", "sh", "-c", cmd, NULL);
                                perror("cannot exec shell!");
                                exit(1);
 
                default:        /* We are the parent */
                                *readfd = rdpipe[0];
                                close(rdpipe[1]);
 
                                *writefd = wrpipe[1];
                                close(wrpipe[0]);
                                return(pid);
        }
        /*NOTREACHED*/
        return(-1);
}                                               


Hope this helps...  [I specifically use it with telnet...]

	-- Alan Robertson
	   alanr at suse.com