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From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.wizards
Subject: Re: Saving stderr output in memory
Message-ID: <5981@star.cs.vu.nl>
Date: 15 Mar 90 00:09:58 GMT
References: <14020086@hpisod2.HP.COM> <7406@jpl-devvax.JPL.NASA.GOV>
Sender: news@cs.vu.nl
Reply-To: maart@cs.vu.nl (Maarten Litmaath)
Organization: VU Informatika, Amsterdam, the Netherlands
Lines: 104

In article <7406@jpl-devvax.JPL.NASA.GOV>,
	lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) writes:
)...
)When prog1 dies, the child appends the collected error messages to stdout,
)plus the exit status.  Your program then looks for the magic lines at the
)end of the ordinary stdout output.  [...]

"Yech! This stuff tastes like poison."

Variably-sized buffered IO etc. is left as an exercise.
--------------------cut here--------------------
#include	<stdio.h>

#define		OUT_SIZE	(10 * 1024)
#define		ERR_SIZE	1024

char	*Prog[] = {
	"/bin/cat",
	"/etc/passwd",
	"/non-existent",
	0
};

main()
{
	int	pp_out[2], pp_err[2], pp[2], n_out, n_err, n, pid1, pid2, w;
	int	status;		/* allright, so it should be a union wait */
	char	out[OUT_SIZE], err[ERR_SIZE], *p;


	if (pipe(pp_out) < 0 || pipe(pp_err) < 0)
		panic("pipe");

	switch (pid1 = fork()) {
	case -1:
		panic("fork");
	case 0:
		dup2(pp_out[1], 1); close(pp_out[1]); close(pp_out[0]);
		dup2(pp_err[1], 2); close(pp_err[1]); close(pp_err[0]);
		execv(*Prog, Prog);
		panic(*Prog);
	}

	close(pp_out[1]); close(pp_err[1]);

	if (pipe(pp) < 0)
		panic("pipe");

	switch (pid2 = fork()) {
	case -1:
		panic("fork");
	case 0:
		for (p = err; p < err + sizeof err; p += n)
			if ((n = read(pp_err[0], p, (err + sizeof err) - p))
				<= 0)
				break;
		if (p > err && write(pp[1], err, p - err) < 0)
			panic("write");
		if (n < 0)
			panic("read");
		exit(0);
	}

	close(pp_err[0]); close(pp[1]);

	for (p = out; p < out + sizeof out; p += n)
		if ((n = read(pp_out[0], p, (out + sizeof out) - p)) <= 0)
			break;
	if (n < 0)
		panic("read");
	n_out = p - out;

	for (p = err; p < err + sizeof err; p += n)
		if ((n = read(pp[0], p, (err + sizeof err) - p)) <= 0)
			break;
	if (n < 0)
		panic("read");
	n_err = p - err;

	close(pp_out[0]); close(pp[0]);

	for (n = 0; n < 2; ) {
		w = wait(&status);
		if (w == pid1 || w == pid2) {
			if (w == pid1)
				printf("status: %d\n\n", status >> 8);
			++n;
		}
	}

	printf("out:\n%s\nerr:\n%s", out, err);
}


panic(message)
char	*message;
{
	perror(message);
	exit(1);
}
--------------------cut here--------------------
--
 1) Will 4.5BSD have wait5()?         |Maarten Litmaath @ VU Amsterdam:
 2) Sleep(3) should be sleep(2) again.|maart@cs.vu.nl, uunet!mcsun!botter!maart