Programming

int system_new(const char *comm) {
    int fd[2], status, pid; 
    if (pipe(fd) < 0) { 
        perror("pipe failed"); 
        return ((int) NULL);
    }
    if ((pid = fork()) == 0) { 
        close(fd[0]); close(fd[1]);
        execl("/bin/sh", "/bin/sh", "-c", comm, NULL); 
        perror("couldn't execl"); exit(127); 
    }
    else if (pid > 0) { 
        close(fd[0]); close(fd[1]); 
        wait(&status); 
    }
    else { 
        close(fd[0]); close(fd[1]);
        perror("fork failed"); exit(-1); 
    }
    return WEXITSTATUS(status); 
}

sigset_t new, old;
sigemptyset (&new);
sigaddset(&new, SIGCHLD);
sigprocmask(SIG_BLOCK, &new, &old);

...

// in child, undo by setting to the old mask
sigprocmask(SIG_SETMASK&old, NULL);