sex.c

#include <stdio.h>
#include <unistd.h>

#define PERROR_AND_DIE(_x_) {perror(_x_); _exit(1);}

int main(int argc, char **argv) {
        int fd0[2];
        int fd1[2];


        if ( argc != 3 ) {
                fprintf(stdout, "Usage %s: \"[command 1]\" \"[command 2]\"\n", argv[0]);
                _exit(1);
        }

        if ( pipe(fd0) || pipe(fd1) ) PERROR_AND_DIE("pipe")

        pid_t id = fork();
        if ( id == -1 ) PERROR_AND_DIE("fork");

        if ( id ) {
                if ( -1 == close(0) )  PERROR_AND_DIE("P1: close 0");
                if ( -1 == dup2(fd0[0], 0) ) PERROR_AND_DIE("P1: dup 0"); //Read my STDIN from this pipe

                if ( -1 == close(1) )  PERROR_AND_DIE("P1: close 1");
                if ( -1 == dup2(fd1[1], 1) ) PERROR_AND_DIE("P1: dup 1"); //Write my STDOUT here
                execl("/bin/sh", "/bin/sh", "-c", argv[1], NULL);
                PERROR_AND_DIE("P1: exec")
        }

        if ( -1 == close(0) )  PERROR_AND_DIE("P2: close 0");
        if ( -1 == dup2(fd1[0], 0) ) PERROR_AND_DIE("P2: dup 0");

        if ( -1 == close(1) )  PERROR_AND_DIE("P2: close 1");
        if ( -1 == dup2(fd0[1], 1) ) PERROR_AND_DIE("P2: dup 1");


        execl("/bin/sh", "/bin/sh", "-c", argv[2], NULL);
        PERROR_AND_DIE("P2: exec")
}