#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

/* this shows how a private fork-based popen2() can be used instead of built-in popen */

FILE * popen2(const char *program, const char *type);
int pclose2(FILE *iop);

int main()
{
	char buff[41];
	FILE* f;

	f = popen2("pwd", "r");

	if(!f)
	{
		printf("popen2 error\n");
		return 1;
	}

	while(fgets(buff, 40, f))
		printf("read: %s\n", buff);

	printf("pclose2 returned: %d\n", pclose2(f));
	return 0;
}



////////////////////////////////////////////////////////
// private popen2() - in-fact this is exact copy of
// newlib/libc/posix.c/popen.c with fork() instead of vfork()

static struct pid {
	struct pid *next;
	FILE *fp;
	pid_t pid;
} *pidlist; 
	
FILE * popen2(const char *program, const char *type)
{
	struct pid *cur;
	FILE *iop;
	int pdes[2], pid;

       if ((*type != 'r' && *type != 'w')
	   || (type[1]
	       && (type[2] || (type[1] != 'b' && type[1] != 't'))
			       )) {
		errno = EINVAL;
		return (NULL);
	}

	if ((cur = malloc(sizeof(struct pid))) == NULL)
		return (NULL);

	if (pipe(pdes) < 0) {
		free(cur);
		return (NULL);
	}

	switch (pid = fork()) {
	case -1:			/* Error. */
		(void)close(pdes[0]);
		(void)close(pdes[1]);
		free(cur);
		return (NULL);
		/* NOTREACHED */
	case 0:				/* Child. */
		if (*type == 'r') {
			if (pdes[1] != STDOUT_FILENO) {
				(void)dup2(pdes[1], STDOUT_FILENO);
				(void)close(pdes[1]);
			}
			(void) close(pdes[0]);
		} else {
			if (pdes[0] != STDIN_FILENO) {
				(void)dup2(pdes[0], STDIN_FILENO);
				(void)close(pdes[0]);
			}
			(void)close(pdes[1]);
		}
		execl("/bin/sh", "sh", "-c", program, NULL);
		/* On cygwin32, we may not have /bin/sh.  In that
                   case, try to find sh on PATH.  */
		execlp("sh", "sh", "-c", program, NULL);
		_exit(127);
		/* NOTREACHED */
	}

	/* Parent; assume fdopen can't fail. */
	if (*type == 'r') {
		iop = fdopen(pdes[0], type);
		(void)close(pdes[1]);
	} else {
		iop = fdopen(pdes[1], type);
		(void)close(pdes[0]);
	}

	/* Link into list of file descriptors. */
	cur->fp = iop;
	cur->pid =  pid;
	cur->next = pidlist;
	pidlist = cur;

	return (iop);
}

/*
 * pclose --
 *	Pclose returns -1 if stream is not associated with a `popened' command,
 *	if already `pclosed', or waitpid returns an error.
 */

int pclose2(FILE *iop)
{
	register struct pid *cur, *last;
	int pstat;
	pid_t pid;

	(void)fclose(iop);

	/* Find the appropriate file pointer. */
	for (last = NULL, cur = pidlist; cur; last = cur, cur = cur->next)
		if (cur->fp == iop)
			break;
	if (cur == NULL)
		return (-1);

	do {
		pid = waitpid(cur->pid, &pstat, 0);
	} while (pid == -1 && errno == EINTR);

	/* Remove the entry from the linked list. */
	if (last == NULL)
		pidlist = cur->next;
	else
		last->next = cur->next;
	free(cur);
		
	return (pid == -1 ? -1 : pstat);
}