Redirecting STDOUT to STDIN of a child process

This is a discussion on Redirecting STDOUT to STDIN of a child process within the Linux Programming forums, part of the Platform Specific Boards category; Hello, I'm trying to implement a basic shell in c, and so far i have the basic functions and command ...

  1. #1
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    Redirecting STDOUT to STDIN of a child process

    Hello, I'm trying to implement a basic shell in c, and so far i have the basic functions and command line input working great, and the & works find, however I'm trying to get pipes to work, my problem is that I'm getting a SIGPIPE when using the pipes

    here is a code snip it:
    Code:
    /* Fork the process to allow program being executed a new PID and 
     * Protect the integrity of the shell process.
     */
      pid = fork();
      pipe(data_pipe);   
      switch (pid) 
      {
         case -1:	/* fork failed. */
            perror("fork");
            return 0;
         case 0:		/* inside child process.  */
            close(STDIN_FILENO);
            dup2(data_pipe[1],STDIN_FILENO);
            close(data_pipe[0]);
            //close(data_pipe[1]); // may or may not need to do this... 
              
         /* creat a new command struct so we dont over write parent
          * processes shared memory
          */ 
            struct command_t command2;
            int lcv = 0;
    
           /* Initalize the command structure and allocate into memory */
            command2.name =  (char*)malloc(MAX_ARG_LEN);
            command2.argc = 0;
            command2.opv = (char*)malloc(MAX_ARG_LEN);
            for(lcv=0; lcv<MAX_ARGS;lcv++)
            {  command2.argv[lcv] = (char*)malloc(MAX_ARG_LEN);
            }          
                
            strcat(command->opv,"\n");    // hack job to make parsing work
     
            exeCommand(pathv,&command2,&command->opv);
                
         default:	/* inside parent process. */
            close(STDOUT_FILENO);
            dup2(data_pipe[1],STDOUT_FILENO);
            close(data_pipe[0]);
            //close(data_pipe[1]); // may or may not be needed.
            execvp(command->name,command->argv);
      }
    I've been working on this for days because from what i can tell it should be working fine... but I'm kinda new to some of these things so I'm sure I'm missing it. heck i might be doing this entirely wrong for all i know , i didn't want to post here cuz well i wanted to figure it out on my own but after a couple of days i'm starting get sleepy. if all the coded is needed i can post that too...

    any help anyone can offer would be much appreciated.
    Last edited by 0xception; 09-13-2005 at 10:51 PM.

  2. #2
    cwr
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    This belongs in Linux programming.

  3. #3
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    What you are doing now is

    child

    close stdin
    make pipeout as stdin
    close pipein

    parent

    close stdout
    make pipeout as stdout
    close pipein
    what you need to do is

    child

    close stdout
    make pipeout as stdout
    close stdin
    execute the command

    parent
    close stdin
    make pipein as stdin
    close pipeout
    execute the command

  4. #4
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    Also, checkout this

    Pipes

  5. #5
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    Okay thanks a lot for the replay i'll give that switch around a try and read up at that site, looks useful (bookmarked now)

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