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Full Discussion: Help with piping program
Top Forums Programming Help with piping program Post 302112730 by PuppyHusher on Thursday 29th of March 2007 10:34:03 PM
Old 03-29-2007
Help with piping program
Hi, I am trying to write a program that will pipe any number of programs together like in the linux shell. As an example, the below code tries to execute "cat data | grep int | cut -b 1-10." The problem is that the programs never get executed for some reason. It seems like the first program executes, then nothing. Does anyone know what is wrong with this? Thanks.

Code:
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

void run_pipe(char  **command);
int  pipes[4], pipeline;

int main(void){
	
	char* cmd1[]={"cat",  "data", NULL};
	char* cmd2[]={"grep", "int" , NULL};
	char* cmd3[]={"cut",  "-b", "1-10", NULL};
	
	pipeline = 0;
	pipe(pipes);
	pipe(pipes + 2);
	
	run_pipe(cmd1);	
	run_pipe(cmd2);
	run_pipe(cmd3);
}

void run_pipe(char  **command){
  	int status, j;

  	if (!command)	return;

	switch (pipeline){
		case 0:	dup2(pipes[1], 1);	break;

		case 1:	
                     pipe(pipes + 2);
                     dup2(pipes[0], 0);
                     dup2(pipes[3], 1);
                     break;

		case 2:	
                     pipe(pipes);
                     dup2(pipes[2], 0);
                     dup2(pipes[1], 1);
                     break;

	}  for (j=0; j<4; j++) 
		close(pipes[j]);

	if (fork() == 0){
		execvp(*command, command);
	}

	wait(&status);

	pipeline++;
	if (pipeline == 3)	pipeline = 1;
}

 

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LEARN ABOUT HPUX

pipe

pipe(2) 							System Calls Manual							   pipe(2)

NAME

       pipe() - create an interprocess channel

SYNOPSIS

DESCRIPTION

       creates	an  I/O  mechanism  called  a pipe and returns two file descriptors, fildes[0] and fildes[1].  fildes[0] is opened for reading and
       fildes[1] is opened for writing.

       A read-only file descriptor fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis.  For details of the  I/O
       behavior of pipes see read(2) and write(2).

       By  default,  HP-UX  pipes are not STREAMS-based.  It is possible to generate the kernel so that all pipes created on a system are STREAMS-
       based.  This can only be done for HP-UX releases 10.0 and later.  STREAMS-based FIFOs (created by or are not supported on HP-UX.

       To generate a kernel that supports STREAMS-based pipes:

	 o  STREAMS/UX must be installed.

	 o  The module and the driver must be included in the file.  (When STREAMS/UX is installed, and are  automatically  added  to  the  system
	    file.)

	 o  The  tunable  parameter  (see  streampipes(5))  must  be  set  to  1  in the file.	(This is not automatically done when STREAMS/UX is
	    installed.)

	 o  The kernel must be generated and the system rebooted.  Once this is done, all pipes created by will be STREAMS-based.

       For more information, see

EXAMPLES

       The following example uses to implement the command string

RETURN VALUE

       returns one of the following values:

	      Successful completion.

	      Failure.
		     is set to indicate the error.

ERRORS

       sets to one of the following error values if the corresponding condition is true.

       or more file descriptors are currently open.

       The system file table is full.

       The file system lacks sufficient space to create the pipe.

       Could not allocate resources for both Stream heads
		      (STREAMS-based pipes only).

SEE ALSO

       sh(1), read(2), write(2), popen(3S), privileges(5), streampipes(5), streamio(7).

STANDARDS CONFORMANCE

																	   pipe(2)
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