Need help w/ shell handling 3 commands/2 pipes

sptchamp · 07-15-2004, 07:05 PM

I'm trying to write a shell in C that will take 3 commands linked together with 2 pipes. Here's what I have so far but the middle function sees a bad descriptor. Can anyone help?

PHP Code:


			
 int runPipes3(cmd_type *cmd1, cmd_type *cmd2, cmd_type *cmd3)

{

    int fds1[2];

    int fds2[2];

    int pid1;

    int pid2;

    int pid3;

    int status;

    char *pathname1 = getPath(cmd1->argv[0]);

    char *pathname2 = getPath(cmd2->argv[0]);

    char *pathname3 = getPath(cmd3->argv[0]);



    if(pipe(fds1) == -1)

    {

        printf("ERROR: pipe()\n");

        return 1;

    }

    if(pipe(fds2) == -1)

    {

        printf("ERROR: pipe()\n");

        return 1;

    }



    if((pid1 = fork()) < 0)

    {

        printf("ERROR: pipe()\n");

        return 1;

    }

    if(pid1 == 0)

    {

        //3rd process

        close(fds1[1]);

        dup2(fds1[0], 0);

//        close(fds1[0]);

        execv(pathname3, cmd3->argv);

        printf("ERROR: execv()\n");

        return 1;

    }

    else

    {

        //parent process

        //need to fork again, so the shell isn't replaced

        if((pid2 = fork()) < 0)

        {

            printf("ERROR: fork()\n");

            return 1;

        }

        if(pid2 == 0)

        {

//            close(fds2[0]);

//            close(fds1[1]);

            dup2(fds2[1], 0);

            dup2(fds1[0], 1);

            execv(pathname2, cmd2->argv);

            printf("ERROR: fork()\n");

            return 1;

        }

        else

        {

            if((pid3 = fork()) < 0)

            {

                printf("ERROR: fork()\n");

                return 1;

            }

            if(pid3 == 0)

            {

                //1st process

                close(fds2[0]);

                dup2(fds2[1], 1);

//                 close(fds2[1]);

                execv(pathname1, cmd1->argv);

                printf("ERROR: fork()\n");

                return 1;

            }

            else

            {

                //parent process (the shell)

                close(fds1[0]);

                close(fds1[1]);

                close(fds2[0]);

                close(fds2[1]);

                if(cmd3->bckgnd == 0)

                    while(wait(&status) != pid3);

                if(cmd2->bckgnd == 0)

                    while(wait(&status) != pid2);

                if(cmd1->bckgnd == 0)

                    while(wait(&status) != pid1);

            }

        }

    }

    return 0;

}

itsme86 · 07-15-2004, 08:26 PM

Which is the "middle function"?

sptchamp · 07-15-2004, 09:01 PM

ls | cat | wc, cat would be the middle function. Sorry, I should've said process.

infamous41md · 07-15-2004, 09:37 PM

you should try a an approach that works on any number of pipelined processes. you should have an array of pipes, pipes[NPIPES][2]. after u have a command line, go thru and for each pipe fork a child, duplicate descriptors, and execute the command. to control when to duplicate descriptors, well you know that every child after the first will have its standard input duplicated, and every command except the last has its output duplicated. something that is very informative is
$ strace -vf /bin/sh ls | sort | grep -v bla