[ale] ptr example

[cfowler]

Compile with gcc -o pshell pshell.c

If ttyp0 is free, this will show you how it works.

One thing to remeber is that Linux now uses pty98 as the new standard. 
These are pseudos found in /dev/pts.  This code supports the old names
but it is still the same.




#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <termios.h>
#include <sys/select.h>

#define SHELL "/bin/sh"


int
main(int argc, char *argv[]) {
        int mfd, sfd;
        int pid;
        fd_set fds;
        struct termios old, new;


        if((mfd = open("/dev/ptyp0", O_RDWR)) == -1) {
                perror("Open master");
                exit(1);
        }

        if((sfd = open("/dev/ttyp0", O_RDWR)) == -1) {
                perror("Open slave");
                exit(1);
        }

        switch(pid = fork()) {
                case -1:
                        perror("fork");
                        exit(1);
                case 0: // Child
                        setsid();
                        close(0); close(1); close(2);
                        dup2(sfd, 0); 
                        dup2(sfd, 1);
                        dup2(sfd, 2);
                        execl(SHELL, SHELL, 0);
                        perror("exec");
                        exit(1);
                default: // parent
                        break;

        }

        close(sfd);

        // Make or terminal raw!
        tcgetattr(1, &old);
        new = old;
        cfmakeraw(&new);
        tcsetattr(1, TCSANOW, &new);

        while(1) {
                char b;

                FD_ZERO(&fds);
                FD_SET(mfd, &fds);
                FD_SET(0, &fds);

                select(mfd + 1, &fds, NULL, NULL, NULL);

                if(FD_ISSET(mfd, &fds)) {
                        if(read(mfd, &b, 1) <=0) {
                                        tcsetattr(0, TCSANOW, &old);
                                        exit(0);
                        }
                        write(0, &b, 1);
                }

                if(FD_ISSET(0, &fds)) {
                        read(0, &b, 1);
                        write(mfd, &b, 1);
                }
        }
        

}
/* vi: set ts=4 sw=4:*/

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