Simulating Pipe in C.

 you will probably need to do a

man fork
and man exec too

man 2 pipe
man 2 fork
man 2 execlp
man 2 dup2
do the math by Yourself

This is what I have thus far:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

int main(int arg, char *argv[]) {
   FILE *fpipe;
   char *command = argv[1];
   char line[256];

   if ( !(fpipe = (FILE*)popen(command,"r")) )
   {  // If fpipe is NULL
      perror("Problems with pipe");
      exit(1);
   }


   while ( fgets( line, sizeof line, fpipe))
   {
     printf("%s", line);
   } pclose(fpipe);

Now I can't figure out how exactly to pipe the output into another command. I've tried execve, but to no avial since it can't take argv[] as an argument. I am looking into raven's idea as well.

since you have two commands you will need to fork() to create a new process after you do a popen.

so in one process you close the read end of the pipe and in the other you close the write end
and then you can use the pipe for one way communication.

> since you have two commands you will need to fork() to create a new process after you do a popen.
and duplicate fd obtained from popen to stdout(stdin)

>> since you have two commands you will need to fork() to create a new process after you do a popen.

If your popen implementation is standards compliant, popen should already do that for you, so there's no need for an extra fork.

However, using a combination of pipe, fork, read and write is a good alternative.

Infinity08: You missed one point
pipe <prog1> <prog1>
You haveto replace Your application with prog1(and duplicate stdin/out from proper fds), or act as proxy between two popen()s - right?

>> Infinity08: You missed one point

I don't think I did ... you only have to set up a one-way stream from prog2's stdout to prog1's stdin, and that can easily be done with two popen's.

So, I'm not sure what I missed ?

But You are executing from pipe program right? So You have two FILE structures and have to act as proxy. Right?
But there's much easier/lighter solution - pipe(), fork(), dup2()x2, exec()x2 - isn't it?

>> But there's much easier/lighter solution - pipe(), fork(), dup2()x2, exec()x2 - isn't it?

I would prefer it too, but it's not easier, because popen does the fork's and exec's for you - you just have to popen the two processes - one for reading and one for writing, and then loop over the data and forward ...

Unless the following is allowed usage, then popen(one way pipe) is useless
cat /etc/passwd | pipe cat tail | cat

> % pipe "cat /etc/passwd" "wc -l"
But I agree, that tokeninzing params for exec() usage is not easier at all.
BTW: system("argv[1] | argv[2]") // LOL ;)